diff --git a/.clang-tidy b/.clang-tidy
index e42e75cde28..21d190190af 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -1,5 +1,5 @@
 ---
-Checks: '-*,readability-container-size-empty,readability-implicit-bool-cast,readability-implicit-bool-conversion,modernize-use-equals-default,modernize-use-override,modernize-use-using,readability-braces-around-statements,modernize-use-nullptr,performance-move-const-arg,cppcoreguidelines-pro-type-member-init,cppcoreguidelines-init-variables,clang-analyzer-optin.cplusplus.UninitializedObject,readability-operators-representation'
+Checks: '-*,readability-container-size-empty,readability-implicit-bool-cast,readability-implicit-bool-conversion,modernize-concat-nested-namespaces,modernize-use-equals-default,modernize-use-override,modernize-use-using,readability-braces-around-statements,modernize-use-nullptr,performance-move-const-arg,cppcoreguidelines-pro-type-member-init,cppcoreguidelines-init-variables,clang-analyzer-optin.cplusplus.UninitializedObject,readability-operators-representation'
 HeaderFilterRegex: '.*(?<!nlohmann\/json)\.(hpp|cpp|ipp)$'
 AnalyzeTemporaryDtors: true
 CheckOptions:
diff --git a/Alignment/include/ActsAlignment/Kernel/detail/AlignmentEngine.hpp b/Alignment/include/ActsAlignment/Kernel/detail/AlignmentEngine.hpp
index 225357c0486..64e7f9c0eb7 100644
--- a/Alignment/include/ActsAlignment/Kernel/detail/AlignmentEngine.hpp
+++ b/Alignment/include/ActsAlignment/Kernel/detail/AlignmentEngine.hpp
@@ -19,8 +19,7 @@
 
 #include <unordered_map>
 
-namespace ActsAlignment {
-namespace detail {
+namespace ActsAlignment::detail {
 
 using namespace Acts;
 ///
@@ -299,5 +298,4 @@ TrackAlignmentState trackAlignmentState(
   return alignState;
 }
 
-}  // namespace detail
-}  // namespace ActsAlignment
+}  // namespace ActsAlignment::detail
diff --git a/Alignment/src/Kernel/detail/AlignmentEngine.cpp b/Alignment/src/Kernel/detail/AlignmentEngine.cpp
index 552bba03b90..c5c012d08d7 100644
--- a/Alignment/src/Kernel/detail/AlignmentEngine.cpp
+++ b/Alignment/src/Kernel/detail/AlignmentEngine.cpp
@@ -8,8 +8,7 @@
 
 #include "ActsAlignment/Kernel/detail/AlignmentEngine.hpp"
 
-namespace ActsAlignment {
-namespace detail {
+namespace ActsAlignment::detail {
 
 void resetAlignmentDerivative(Acts::AlignmentToBoundMatrix& alignToBound,
                               AlignmentMask mask) {
@@ -33,5 +32,4 @@ void resetAlignmentDerivative(Acts::AlignmentToBoundMatrix& alignToBound,
   }
 }
 
-}  // namespace detail
-}  // namespace ActsAlignment
+}  // namespace ActsAlignment::detail
diff --git a/CI/clang_tidy/limits.yml b/CI/clang_tidy/limits.yml
index 0b75c0fc149..5b2818d7d0e 100644
--- a/CI/clang_tidy/limits.yml
+++ b/CI/clang_tidy/limits.yml
@@ -5,6 +5,7 @@ limits:
   "readability-braces-around-statements": 0
   "readability-implicit-bool-cast": 0
   "readability-implicit-bool-conversion": 0
+  "modernize-concat-nested-namespaces": 0
   "modernize-use-using": 0
   "modernize-use-override": 0
   "modernize-use-equals-default" : 0
diff --git a/Core/include/Acts/Detector/Blueprint.hpp b/Core/include/Acts/Detector/Blueprint.hpp
index 4b63b351ec4..f3ddc47699b 100644
--- a/Core/include/Acts/Detector/Blueprint.hpp
+++ b/Core/include/Acts/Detector/Blueprint.hpp
@@ -20,8 +20,7 @@
 #include <string>
 #include <vector>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 class IGeometryIdGenerator;
 class IInternalStructureBuilder;
@@ -122,5 +121,4 @@ struct Node final {
 };
 
 }  // namespace Blueprint
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/CuboidalContainerBuilder.hpp b/Core/include/Acts/Detector/CuboidalContainerBuilder.hpp
index df385879758..9ec69348116 100644
--- a/Core/include/Acts/Detector/CuboidalContainerBuilder.hpp
+++ b/Core/include/Acts/Detector/CuboidalContainerBuilder.hpp
@@ -19,8 +19,7 @@
 #include <string>
 #include <vector>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 class IRootVolumeFinderBuilder;
 class IGeometryIdGenerator;
@@ -106,5 +105,4 @@ class CuboidalContainerBuilder : public IDetectorComponentBuilder {
   std::unique_ptr<const Logger> m_logger;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/CylindricalContainerBuilder.hpp b/Core/include/Acts/Detector/CylindricalContainerBuilder.hpp
index eb58806015b..c3023cea84e 100644
--- a/Core/include/Acts/Detector/CylindricalContainerBuilder.hpp
+++ b/Core/include/Acts/Detector/CylindricalContainerBuilder.hpp
@@ -21,8 +21,7 @@
 #include <string>
 #include <vector>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 class IRootVolumeFinderBuilder;
 class IGeometryIdGenerator;
@@ -109,5 +108,4 @@ class CylindricalContainerBuilder : public IDetectorComponentBuilder {
   std::unique_ptr<const Logger> m_logger;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/DetectorBuilder.hpp b/Core/include/Acts/Detector/DetectorBuilder.hpp
index 2638f20a28f..6ec5dea54d8 100644
--- a/Core/include/Acts/Detector/DetectorBuilder.hpp
+++ b/Core/include/Acts/Detector/DetectorBuilder.hpp
@@ -15,8 +15,7 @@
 #include <memory>
 #include <string>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 class IGeometryIdGenerator;
 
@@ -69,5 +68,4 @@ class DetectorBuilder final : public IDetectorBuilder {
   std::unique_ptr<const Logger> m_logger;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/DetectorVolumeBuilder.hpp b/Core/include/Acts/Detector/DetectorVolumeBuilder.hpp
index f1a9ef6906a..c7b4ae8c6f6 100644
--- a/Core/include/Acts/Detector/DetectorVolumeBuilder.hpp
+++ b/Core/include/Acts/Detector/DetectorVolumeBuilder.hpp
@@ -17,8 +17,7 @@
 #include <memory>
 #include <string>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 class IExternalStructureBuilder;
 class IInternalStructureBuilder;
 class IGeometryIdGenerator;
@@ -79,5 +78,4 @@ class DetectorVolumeBuilder : public IDetectorComponentBuilder {
   std::unique_ptr<const Logger> m_logger;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/GeometryCompatibilityConcept.hpp b/Core/include/Acts/Detector/GeometryCompatibilityConcept.hpp
index f58a8223435..4879fb9533d 100644
--- a/Core/include/Acts/Detector/GeometryCompatibilityConcept.hpp
+++ b/Core/include/Acts/Detector/GeometryCompatibilityConcept.hpp
@@ -12,9 +12,7 @@
 #include "Acts/Geometry/TrackingVolume.hpp"
 #include "Acts/Utilities/TypeTraits.hpp"
 
-namespace Acts {
-
-namespace Concepts {
+namespace Acts::Concepts {
 
 // Types to check compatibility of
 template <typename propagator_state_t, typename navigator_t>
@@ -48,6 +46,4 @@ template <typename propagator_state_t, typename navigator_t>
 constexpr bool NavigationCompatibilityConcept =
     NavigationCompatibilityConceptImpl<propagator_state_t, navigator_t>::value;
 
-}  // namespace Concepts
-
-}  // namespace Acts
+}  // namespace Acts::Concepts
diff --git a/Core/include/Acts/Detector/GeometryIdMapper.hpp b/Core/include/Acts/Detector/GeometryIdMapper.hpp
index 00037f26497..f4d6a4163b2 100644
--- a/Core/include/Acts/Detector/GeometryIdMapper.hpp
+++ b/Core/include/Acts/Detector/GeometryIdMapper.hpp
@@ -16,8 +16,7 @@
 
 #include <map>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 /// @brief This is a mapper of geometry ids, which can be used to
 /// assign predefined geometry ids to objects
@@ -144,5 +143,4 @@ class GeometryIdMapper final : public IGeometryIdGenerator {
   std::unique_ptr<const Logger> m_logger;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/IndexedRootVolumeFinderBuilder.hpp b/Core/include/Acts/Detector/IndexedRootVolumeFinderBuilder.hpp
index e817ce599c5..6160216c2d5 100644
--- a/Core/include/Acts/Detector/IndexedRootVolumeFinderBuilder.hpp
+++ b/Core/include/Acts/Detector/IndexedRootVolumeFinderBuilder.hpp
@@ -16,9 +16,7 @@
 #include <memory>
 #include <vector>
 
-namespace Acts {
-
-namespace Experimental {
+namespace Acts::Experimental {
 
 class DetectorVolume;
 
@@ -45,5 +43,4 @@ class IndexedRootVolumeFinderBuilder final : public IRootVolumeFinderBuilder {
   std::vector<Acts::BinningValue> m_casts;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/KdtSurfacesProvider.hpp b/Core/include/Acts/Detector/KdtSurfacesProvider.hpp
index 75ec9d050e6..dda69aeefc7 100644
--- a/Core/include/Acts/Detector/KdtSurfacesProvider.hpp
+++ b/Core/include/Acts/Detector/KdtSurfacesProvider.hpp
@@ -20,9 +20,7 @@
 #include <tuple>
 #include <vector>
 
-namespace Acts {
-
-namespace Experimental {
+namespace Acts::Experimental {
 
 /// @brief A wrapper class around a KDTree of surfaces
 ///
@@ -195,6 +193,4 @@ class KdtSurfacesProvider : public ISurfacesProvider {
   Extent m_region;
 };
 
-}  // namespace Experimental
-
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/LayerStructureBuilder.hpp b/Core/include/Acts/Detector/LayerStructureBuilder.hpp
index 542e1f4a44b..afc04463cc5 100644
--- a/Core/include/Acts/Detector/LayerStructureBuilder.hpp
+++ b/Core/include/Acts/Detector/LayerStructureBuilder.hpp
@@ -28,8 +28,7 @@
 #include <string>
 #include <vector>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 /// @brief This is a builder of layer structures to be contained
 /// within a DetectorVolume, it extends the IInternalStructureBuilder
@@ -130,5 +129,4 @@ class LayerStructureBuilder : public IInternalStructureBuilder {
   std::unique_ptr<const Logger> m_logger;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/MultiWireStructureBuilder.hpp b/Core/include/Acts/Detector/MultiWireStructureBuilder.hpp
index e58ce69290c..86cce7fce56 100644
--- a/Core/include/Acts/Detector/MultiWireStructureBuilder.hpp
+++ b/Core/include/Acts/Detector/MultiWireStructureBuilder.hpp
@@ -21,8 +21,7 @@
 #include <string>
 #include <vector>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 class MultiWireStructureBuilder {
  public:
@@ -75,5 +74,4 @@ class MultiWireStructureBuilder {
   std::unique_ptr<const Acts::Logger> mLogger;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/ProtoBinning.hpp b/Core/include/Acts/Detector/ProtoBinning.hpp
index 2122c61d51c..f3adb4e0779 100644
--- a/Core/include/Acts/Detector/ProtoBinning.hpp
+++ b/Core/include/Acts/Detector/ProtoBinning.hpp
@@ -18,9 +18,7 @@
 #include <string>
 #include <vector>
 
-namespace Acts {
-
-namespace Experimental {
+namespace Acts::Experimental {
 
 /// @brief  Simple helper class to define a binning structure
 ///
@@ -146,5 +144,4 @@ struct BinningDescription {
   }
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/ProtoSupport.hpp b/Core/include/Acts/Detector/ProtoSupport.hpp
index e900cae6e2d..e4525523698 100644
--- a/Core/include/Acts/Detector/ProtoSupport.hpp
+++ b/Core/include/Acts/Detector/ProtoSupport.hpp
@@ -19,9 +19,7 @@
 #include <stdexcept>
 #include <vector>
 
-namespace Acts {
-
-namespace Experimental {
+namespace Acts::Experimental {
 /// @brief Support surface building instructions
 ///
 /// There are two ways to build a support surface:
@@ -78,5 +76,4 @@ struct ProtoSupport {
   bool assignToAll = true;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/VolumeStructureBuilder.hpp b/Core/include/Acts/Detector/VolumeStructureBuilder.hpp
index ca2acb79b78..812f2e761ec 100644
--- a/Core/include/Acts/Detector/VolumeStructureBuilder.hpp
+++ b/Core/include/Acts/Detector/VolumeStructureBuilder.hpp
@@ -19,8 +19,7 @@
 #include <optional>
 #include <string>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 /// This class provides the external detector volume structure, configured
 /// either from:
@@ -77,5 +76,4 @@ class VolumeStructureBuilder : public IExternalStructureBuilder {
   std::unique_ptr<const Logger> m_logger;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/detail/BlueprintDrawer.hpp b/Core/include/Acts/Detector/detail/BlueprintDrawer.hpp
index 4b3007fce8c..cc589bf8e06 100644
--- a/Core/include/Acts/Detector/detail/BlueprintDrawer.hpp
+++ b/Core/include/Acts/Detector/detail/BlueprintDrawer.hpp
@@ -13,12 +13,7 @@
 #include <ostream>
 #include <string>
 
-namespace Acts {
-
-namespace Experimental {
-
-namespace detail {
-namespace BlueprintDrawer {
+namespace Acts::Experimental::detail::BlueprintDrawer {
 
 /// @brief Nested options struct for the drawer
 struct Options {
@@ -63,7 +58,4 @@ struct Options {
 void dotStream(std::ostream& ss, const Blueprint::Node& node,
                const Options& options = Options{});
 
-}  // namespace BlueprintDrawer
-}  // namespace detail
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental::detail::BlueprintDrawer
diff --git a/Core/include/Acts/Detector/detail/BlueprintHelper.hpp b/Core/include/Acts/Detector/detail/BlueprintHelper.hpp
index 59dc89d75b3..06cc3e2046f 100644
--- a/Core/include/Acts/Detector/detail/BlueprintHelper.hpp
+++ b/Core/include/Acts/Detector/detail/BlueprintHelper.hpp
@@ -11,12 +11,7 @@
 #include "Acts/Detector/Blueprint.hpp"
 #include "Acts/Utilities/BinningData.hpp"
 
-namespace Acts {
-
-namespace Experimental {
-
-namespace detail {
-namespace BlueprintHelper {
+namespace Acts::Experimental::detail::BlueprintHelper {
 
 /// @brief Sort the nodes in the blueprint container node
 ///
@@ -42,7 +37,4 @@ void fillGapsCylindrical(Blueprint::Node& node, bool adjustToParent = true);
 /// @param adjustToParent nodes, if nodes should be adjusted to parent
 void fillGapsCuboidal(Blueprint::Node& node, bool adjustToParent = true);
 
-}  // namespace BlueprintHelper
-}  // namespace detail
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental::detail::BlueprintHelper
diff --git a/Core/include/Acts/Detector/detail/CuboidalDetectorHelper.hpp b/Core/include/Acts/Detector/detail/CuboidalDetectorHelper.hpp
index c264d645d7e..34be7576be2 100644
--- a/Core/include/Acts/Detector/detail/CuboidalDetectorHelper.hpp
+++ b/Core/include/Acts/Detector/detail/CuboidalDetectorHelper.hpp
@@ -22,15 +22,12 @@
 #include <memory>
 #include <vector>
 
-namespace Acts {
-
-namespace Experimental {
+namespace Acts::Experimental {
 
 class DetectorVolume;
 class Portal;
 
-namespace detail {
-namespace CuboidalDetectorHelper {
+namespace detail::CuboidalDetectorHelper {
 
 /// @brief Connect detector volumes given a binning value
 ///
@@ -81,7 +78,5 @@ std::array<std::vector<ActsScalar>, 3u> xyzBoundaries(
     const std::vector<const DetectorVolume*>& volumes,
     Acts::Logging::Level logLevel = Acts::Logging::INFO);
 
-}  // namespace CuboidalDetectorHelper
-}  // namespace detail
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace detail::CuboidalDetectorHelper
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/detail/CylindricalDetectorHelper.hpp b/Core/include/Acts/Detector/detail/CylindricalDetectorHelper.hpp
index e603c4fb0ef..91b7935482c 100644
--- a/Core/include/Acts/Detector/detail/CylindricalDetectorHelper.hpp
+++ b/Core/include/Acts/Detector/detail/CylindricalDetectorHelper.hpp
@@ -23,15 +23,12 @@
 #include <memory>
 #include <vector>
 
-namespace Acts {
-
-namespace Experimental {
+namespace Acts::Experimental {
 
 class DetectorVolume;
 class Portal;
 
-namespace detail {
-namespace CylindricalDetectorHelper {
+namespace detail::CylindricalDetectorHelper {
 
 /// @brief Connect detector volumes in R
 ///
@@ -240,7 +237,5 @@ std::array<std::vector<ActsScalar>, 3u> rzphiBoundaries(
                                    uniqueBoundaries[2].end())}};
 }
 
-}  // namespace CylindricalDetectorHelper
-}  // namespace detail
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace detail::CylindricalDetectorHelper
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/detail/DetectorVolumeConsistency.hpp b/Core/include/Acts/Detector/detail/DetectorVolumeConsistency.hpp
index 5d3c2d2d2ea..ffc9ae97985 100644
--- a/Core/include/Acts/Detector/detail/DetectorVolumeConsistency.hpp
+++ b/Core/include/Acts/Detector/detail/DetectorVolumeConsistency.hpp
@@ -15,13 +15,11 @@
 #include <memory>
 #include <vector>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 class DetectorVolume;
 
-namespace detail {
-namespace DetectorVolumeConsistency {
+namespace detail::DetectorVolumeConsistency {
 
 /// @brief Helper method to check alignment of the volumes, this method checks
 /// if the rotational part of the transform is identical
@@ -52,7 +50,5 @@ std::vector<ActsScalar> checkCenterAlignment(
     const std::vector<std::shared_ptr<Experimental::DetectorVolume>>& volumes,
     BinningValue axisValue);
 
-}  // namespace DetectorVolumeConsistency
-}  // namespace detail
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace detail::DetectorVolumeConsistency
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/detail/IndexedGridFiller.hpp b/Core/include/Acts/Detector/detail/IndexedGridFiller.hpp
index 0311a728743..742d733930f 100644
--- a/Core/include/Acts/Detector/detail/IndexedGridFiller.hpp
+++ b/Core/include/Acts/Detector/detail/IndexedGridFiller.hpp
@@ -26,9 +26,7 @@
 #include <string>
 #include <vector>
 
-namespace Acts {
-namespace Experimental {
-namespace detail {
+namespace Acts::Experimental::detail {
 
 /// @brief Helper method to generate completely populated bin sequences
 /// that respect the boundary type of the axis
@@ -253,6 +251,4 @@ struct IndexedGridFiller {
   const Logger& logger() const { return (*oLogger); }
 };
 
-}  // namespace detail
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental::detail
diff --git a/Core/include/Acts/Detector/detail/IndexedSurfacesGenerator.hpp b/Core/include/Acts/Detector/detail/IndexedSurfacesGenerator.hpp
index fbc510ae854..598945d3e5d 100644
--- a/Core/include/Acts/Detector/detail/IndexedSurfacesGenerator.hpp
+++ b/Core/include/Acts/Detector/detail/IndexedSurfacesGenerator.hpp
@@ -17,9 +17,7 @@
 #include <array>
 #include <memory>
 
-namespace Acts {
-namespace Experimental {
-namespace detail {
+namespace Acts::Experimental::detail {
 
 /// @brief  A templated indexed grid generator.
 ///
@@ -104,6 +102,4 @@ struct IndexedSurfacesGenerator {
   const Logger& logger() const { return *oLogger; }
 };
 
-}  // namespace detail
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental::detail
diff --git a/Core/include/Acts/Detector/detail/PortalHelper.hpp b/Core/include/Acts/Detector/detail/PortalHelper.hpp
index cf178c84968..63eb39ffca6 100644
--- a/Core/include/Acts/Detector/detail/PortalHelper.hpp
+++ b/Core/include/Acts/Detector/detail/PortalHelper.hpp
@@ -36,8 +36,7 @@ using PortalReplacement =
     std::tuple<std::shared_ptr<Experimental::Portal>, unsigned int, Direction,
                std::vector<ActsScalar>, BinningValue>;
 
-namespace detail {
-namespace PortalHelper {
+namespace detail::PortalHelper {
 
 /// @brief Method to attach a single detector volume to a portal
 ///
@@ -108,7 +107,6 @@ stripSideVolumes(
     const std::vector<unsigned int>& selectedOnly = {},
     Acts::Logging::Level logLevel = Acts::Logging::INFO);
 
-}  // namespace PortalHelper
-}  // namespace detail
+}  // namespace detail::PortalHelper
 }  // namespace Experimental
 }  // namespace Acts
diff --git a/Core/include/Acts/Detector/detail/ProtoMaterialHelper.hpp b/Core/include/Acts/Detector/detail/ProtoMaterialHelper.hpp
index 3d8738da423..eb483a2f680 100644
--- a/Core/include/Acts/Detector/detail/ProtoMaterialHelper.hpp
+++ b/Core/include/Acts/Detector/detail/ProtoMaterialHelper.hpp
@@ -18,8 +18,7 @@ namespace Experimental {
 
 struct BinningDescription;
 
-namespace detail {
-namespace ProtoMaterialHelper {
+namespace detail::ProtoMaterialHelper {
 
 /// @brief Method that attaches proto material to a surface given
 /// a proto binning description
@@ -34,7 +33,6 @@ BinningDescription attachProtoMaterial(const GeometryContext& gctx,
                                        Surface& surface,
                                        const BinningDescription& bDescription);
 
-}  // namespace ProtoMaterialHelper
-}  // namespace detail
+}  // namespace detail::ProtoMaterialHelper
 }  // namespace Experimental
 }  // namespace Acts
diff --git a/Core/include/Acts/Detector/detail/ReferenceGenerators.hpp b/Core/include/Acts/Detector/detail/ReferenceGenerators.hpp
index cdd08563f41..ab72f16d62e 100644
--- a/Core/include/Acts/Detector/detail/ReferenceGenerators.hpp
+++ b/Core/include/Acts/Detector/detail/ReferenceGenerators.hpp
@@ -16,9 +16,7 @@
 
 #include <vector>
 
-namespace Acts {
-namespace Experimental {
-namespace detail {
+namespace Acts::Experimental::detail {
 
 /// A struct to access the center position
 ///
@@ -94,6 +92,4 @@ struct PolyhedronReferenceGenerator {
   }
 };
 
-}  // namespace detail
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental::detail
diff --git a/Core/include/Acts/Detector/detail/SupportSurfacesHelper.hpp b/Core/include/Acts/Detector/detail/SupportSurfacesHelper.hpp
index 0f344c0bb81..1cfef5fdb5b 100644
--- a/Core/include/Acts/Detector/detail/SupportSurfacesHelper.hpp
+++ b/Core/include/Acts/Detector/detail/SupportSurfacesHelper.hpp
@@ -24,14 +24,12 @@ namespace Acts {
 
 using namespace UnitLiterals;
 
-namespace Experimental {
-namespace detail {
 /// @brief  This file contains helper methods to build common support structures
 /// such as support cylinders or discs.
 ///
 /// It allows to model those as Disc/CylinderSurface objects, but also - if
 /// configured such - as approximations built from palanr surfaces
-namespace SupportSurfacesHelper {
+namespace Experimental::detail::SupportSurfacesHelper {
 
 using SupportSurfaceComponents =
     std::tuple<Surface::SurfaceType, std::vector<ActsScalar>, Acts::Transform3>;
@@ -161,7 +159,5 @@ void addSupport(std::vector<std::shared_ptr<Surface>>& layerSurfaces,
                 const SurfaceComponentsCreator& componentCreator,
                 unsigned int supportSplits = 1u);
 
-}  // namespace SupportSurfacesHelper
-}  // namespace detail
-}  // namespace Experimental
+}  // namespace Experimental::detail::SupportSurfacesHelper
 }  // namespace Acts
diff --git a/Core/include/Acts/Detector/interface/IDetectorBuilder.hpp b/Core/include/Acts/Detector/interface/IDetectorBuilder.hpp
index 2b09dc7a2e3..73a167e08ba 100644
--- a/Core/include/Acts/Detector/interface/IDetectorBuilder.hpp
+++ b/Core/include/Acts/Detector/interface/IDetectorBuilder.hpp
@@ -12,8 +12,7 @@
 
 #include <memory>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 class Detector;
 
@@ -37,5 +36,4 @@ class IDetectorBuilder {
       const GeometryContext& gctx) const = 0;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/interface/IDetectorComponentBuilder.hpp b/Core/include/Acts/Detector/interface/IDetectorComponentBuilder.hpp
index 5e4cb319ec6..e2b8f5fdd6d 100644
--- a/Core/include/Acts/Detector/interface/IDetectorComponentBuilder.hpp
+++ b/Core/include/Acts/Detector/interface/IDetectorComponentBuilder.hpp
@@ -11,8 +11,7 @@
 #include "Acts/Detector/DetectorComponents.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 /// @brief  This is the interface for detector component builders;
 /// such a builder could be a simple detector volume builder, with
@@ -31,5 +30,4 @@ class IDetectorComponentBuilder {
   virtual DetectorComponent construct(const GeometryContext& gctx) const = 0;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/interface/IExternalStructureBuilder.hpp b/Core/include/Acts/Detector/interface/IExternalStructureBuilder.hpp
index efc55d7e1e7..483ddf6299a 100644
--- a/Core/include/Acts/Detector/interface/IExternalStructureBuilder.hpp
+++ b/Core/include/Acts/Detector/interface/IExternalStructureBuilder.hpp
@@ -11,8 +11,7 @@
 #include "Acts/Detector/DetectorComponents.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 /// @brief This is the interface definition of external structure
 /// builders for DetectorVolume construction.
@@ -28,5 +27,4 @@ class IExternalStructureBuilder {
   virtual ExternalStructure construct(const GeometryContext& gctx) const = 0;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/interface/IInternalStructureBuilder.hpp b/Core/include/Acts/Detector/interface/IInternalStructureBuilder.hpp
index 6d306735ba3..4ae2e242bf0 100644
--- a/Core/include/Acts/Detector/interface/IInternalStructureBuilder.hpp
+++ b/Core/include/Acts/Detector/interface/IInternalStructureBuilder.hpp
@@ -11,8 +11,7 @@
 #include "Acts/Detector/DetectorComponents.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 /// @brief This is the interface definition of internal structure
 /// builders for DetectorVolume construction.
@@ -31,5 +30,4 @@ class IInternalStructureBuilder {
   virtual InternalStructure construct(const GeometryContext& gctx) const = 0;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Detector/interface/IRootVolumeFinderBuilder.hpp b/Core/include/Acts/Detector/interface/IRootVolumeFinderBuilder.hpp
index f2f392ccb79..793c5d8a9b1 100644
--- a/Core/include/Acts/Detector/interface/IRootVolumeFinderBuilder.hpp
+++ b/Core/include/Acts/Detector/interface/IRootVolumeFinderBuilder.hpp
@@ -14,9 +14,7 @@
 #include <memory>
 #include <vector>
 
-namespace Acts {
-
-namespace Experimental {
+namespace Acts::Experimental {
 
 class DetectorVolume;
 
@@ -38,5 +36,4 @@ class IRootVolumeFinderBuilder {
       const = 0;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/EventData/MultiTrajectoryHelpers.hpp b/Core/include/Acts/EventData/MultiTrajectoryHelpers.hpp
index 94bef2db8f7..1bc2c6e6f8b 100644
--- a/Core/include/Acts/EventData/MultiTrajectoryHelpers.hpp
+++ b/Core/include/Acts/EventData/MultiTrajectoryHelpers.hpp
@@ -17,9 +17,7 @@
 #include <functional>
 #include <unordered_map>
 
-namespace Acts {
-
-namespace MultiTrajectoryHelpers {
+namespace Acts::MultiTrajectoryHelpers {
 
 /// @brief Struct for brief trajectory summary info
 ///
@@ -164,6 +162,4 @@ FreeVector freeSmoothed(const GeometryContext& gctx,
   return transformBoundToFreeParameters(trackStateProxy.referenceSurface(),
                                         gctx, trackStateProxy.smoothed());
 }
-}  // namespace MultiTrajectoryHelpers
-
-}  // namespace Acts
+}  // namespace Acts::MultiTrajectoryHelpers
diff --git a/Core/include/Acts/EventData/detail/CalculateResiduals.hpp b/Core/include/Acts/EventData/detail/CalculateResiduals.hpp
index 533745316b3..38adc0df822 100644
--- a/Core/include/Acts/EventData/detail/CalculateResiduals.hpp
+++ b/Core/include/Acts/EventData/detail/CalculateResiduals.hpp
@@ -15,8 +15,7 @@
 
 #include <Eigen/Core>
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 /// Residuals between bound reference parameters and a measured subspace.
 ///
@@ -94,5 +93,4 @@ inline void calculateResiduals(FreeIndices size,
   }
 }
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/EventData/detail/ParameterTraits.hpp b/Core/include/Acts/EventData/detail/ParameterTraits.hpp
index f5e116c88b6..6252a474af2 100644
--- a/Core/include/Acts/EventData/detail/ParameterTraits.hpp
+++ b/Core/include/Acts/EventData/detail/ParameterTraits.hpp
@@ -14,8 +14,7 @@
 #include <cmath>
 #include <cstddef>
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 /// Traits class for an unrestricted parameter.
 struct UnrestrictedParameterTraits {
@@ -172,5 +171,4 @@ struct ParametersTraitsImpl<FreeIndices> {
 template <typename indices_t>
 constexpr std::size_t kParametersSize = ParametersTraitsImpl<indices_t>::kSize;
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/EventData/detail/covariance_helper.hpp b/Core/include/Acts/EventData/detail/covariance_helper.hpp
index 4f6dbe6440b..acc549fcecf 100644
--- a/Core/include/Acts/EventData/detail/covariance_helper.hpp
+++ b/Core/include/Acts/EventData/detail/covariance_helper.hpp
@@ -12,8 +12,7 @@
 
 #include <type_traits>
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 /// @brief check and correct covariance matrix
 ///
 /// @tparam CovMatrix_t The type of covariance matrix
@@ -70,5 +69,4 @@ struct covariance_helper {
   }
 };
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Material/detail/AverageMaterials.hpp b/Core/include/Acts/Material/detail/AverageMaterials.hpp
index dfabeb61de7..5fec5819dc5 100644
--- a/Core/include/Acts/Material/detail/AverageMaterials.hpp
+++ b/Core/include/Acts/Material/detail/AverageMaterials.hpp
@@ -10,8 +10,7 @@
 
 #include "Acts/Material/MaterialSlab.hpp"
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 /// Compute the average properties for a combined slab of two materials.
 ///
@@ -24,5 +23,4 @@ namespace detail {
 /// throughout the slab.
 MaterialSlab combineSlabs(const MaterialSlab& slab1, const MaterialSlab& slab2);
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Navigation/DetectorNavigator.hpp b/Core/include/Acts/Navigation/DetectorNavigator.hpp
index 47d4955347b..894238be91b 100644
--- a/Core/include/Acts/Navigation/DetectorNavigator.hpp
+++ b/Core/include/Acts/Navigation/DetectorNavigator.hpp
@@ -29,8 +29,7 @@
 #include <boost/algorithm/string.hpp>
 #include <boost/container/small_vector.hpp>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 class DetectorNavigator {
  public:
@@ -439,5 +438,4 @@ class DetectorNavigator {
   }
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Navigation/DetectorVolumeFinders.hpp b/Core/include/Acts/Navigation/DetectorVolumeFinders.hpp
index ebaecba4761..afd24ed0e11 100644
--- a/Core/include/Acts/Navigation/DetectorVolumeFinders.hpp
+++ b/Core/include/Acts/Navigation/DetectorVolumeFinders.hpp
@@ -20,8 +20,7 @@
 
 #include <stdexcept>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 struct NoopFinder : public INavigationDelegate {
   inline void update(const GeometryContext& /*gctx*/,
@@ -120,5 +119,4 @@ using IndexedDetectorVolumesImpl =
     IndexedUpdaterImpl<grid_type, IndexedDetectorVolumeExtractor,
                        DetectorVolumeFiller>;
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Navigation/DetectorVolumeUpdaters.hpp b/Core/include/Acts/Navigation/DetectorVolumeUpdaters.hpp
index 4f9a8cf2684..94da589eb11 100644
--- a/Core/include/Acts/Navigation/DetectorVolumeUpdaters.hpp
+++ b/Core/include/Acts/Navigation/DetectorVolumeUpdaters.hpp
@@ -18,8 +18,7 @@
 
 #include <stdexcept>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 class DetectorVolume;
 
@@ -141,5 +140,4 @@ struct BoundVolumesGrid1Impl : public INavigationDelegate {
   }
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Navigation/MultiLayerSurfacesUpdater.hpp b/Core/include/Acts/Navigation/MultiLayerSurfacesUpdater.hpp
index 8bea8df5568..787cad0f22d 100644
--- a/Core/include/Acts/Navigation/MultiLayerSurfacesUpdater.hpp
+++ b/Core/include/Acts/Navigation/MultiLayerSurfacesUpdater.hpp
@@ -17,8 +17,7 @@
 #include <array>
 #include <memory>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 template <typename grid_t, typename path_generator>
 class MultiLayerSurfacesUpdaterImpl : public INavigationDelegate {
@@ -140,6 +139,4 @@ struct PathGridSurfacesGenerator {
   }
 };
 
-}  // namespace Experimental
-
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Navigation/NavigationStateUpdaters.hpp b/Core/include/Acts/Navigation/NavigationStateUpdaters.hpp
index 5e5ea1068d1..89eebdc4b68 100644
--- a/Core/include/Acts/Navigation/NavigationStateUpdaters.hpp
+++ b/Core/include/Acts/Navigation/NavigationStateUpdaters.hpp
@@ -23,9 +23,7 @@
 #include <array>
 #include <memory>
 
-namespace Acts {
-
-namespace Experimental {
+namespace Acts::Experimental {
 
 /// Helper method to update the candidates (portals/surfaces),
 /// this can be called for initial surface/portal estimation,
@@ -201,5 +199,4 @@ class ChainedUpdaterImpl : public INavigationDelegate {
   }
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Navigation/SurfaceCandidatesUpdaters.hpp b/Core/include/Acts/Navigation/SurfaceCandidatesUpdaters.hpp
index 534170ec06e..3c707fcc731 100644
--- a/Core/include/Acts/Navigation/SurfaceCandidatesUpdaters.hpp
+++ b/Core/include/Acts/Navigation/SurfaceCandidatesUpdaters.hpp
@@ -22,8 +22,7 @@
 #include <memory>
 #include <tuple>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 struct AllPortalsImpl : public INavigationDelegate {
   /// A ordered portal provider
@@ -155,5 +154,4 @@ template <typename grid_type, template <typename> class indexed_updator>
 using IndexedSurfacesAllPortalsImpl =
     ChainedUpdaterImpl<AllPortalsImpl, indexed_updator<grid_type>>;
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/Propagator/StepperConcept.hpp b/Core/include/Acts/Propagator/StepperConcept.hpp
index d7e81502939..c62f3127406 100644
--- a/Core/include/Acts/Propagator/StepperConcept.hpp
+++ b/Core/include/Acts/Propagator/StepperConcept.hpp
@@ -21,8 +21,7 @@
 namespace Acts {
 class Surface;
 
-namespace Concepts {
-namespace Stepper {
+namespace Concepts::Stepper {
 
 template <typename T>
 using state_t = typename T::State;
@@ -214,8 +213,7 @@ constexpr bool MultiStepperStateConcept= require<
         };
 // clang-format on
 
-}  // namespace Stepper
-}  // namespace Concepts
+}  // namespace Concepts::Stepper
 
 template <typename stepper, typename state = typename stepper::State>
 constexpr bool StepperConcept =
diff --git a/Core/include/Acts/Propagator/detail/Auctioneer.hpp b/Core/include/Acts/Propagator/detail/Auctioneer.hpp
index 1f0fdce16df..e086526d327 100644
--- a/Core/include/Acts/Propagator/detail/Auctioneer.hpp
+++ b/Core/include/Acts/Propagator/detail/Auctioneer.hpp
@@ -11,8 +11,7 @@
 #include <algorithm>
 #include <array>
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 /// The StepperExtensionList allows to add an arbitrary number of step
 /// evaluation algorithms for the RKN4 evaluation. These can be categorised in
 /// two general types:
@@ -106,5 +105,4 @@ struct HighestValidAuctioneer {
   }
 };
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Propagator/detail/CovarianceEngine.hpp b/Core/include/Acts/Propagator/detail/CovarianceEngine.hpp
index 5f7af7a0cc1..1509402a04b 100644
--- a/Core/include/Acts/Propagator/detail/CovarianceEngine.hpp
+++ b/Core/include/Acts/Propagator/detail/CovarianceEngine.hpp
@@ -21,8 +21,7 @@
 
 #include <tuple>
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 /// @brief These functions perform the transport of a covariance matrix using
 /// given Jacobians. The required data is provided by the stepper object
@@ -147,5 +146,4 @@ Result<BoundTrackParameters> boundToBoundConversion(
     const GeometryContext& gctx, const BoundTrackParameters& boundParameters,
     const Surface& targetSurface, const Vector3& bField = Vector3::Zero());
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Propagator/detail/JacobianEngine.hpp b/Core/include/Acts/Propagator/detail/JacobianEngine.hpp
index e6798262256..8b448cf83d6 100644
--- a/Core/include/Acts/Propagator/detail/JacobianEngine.hpp
+++ b/Core/include/Acts/Propagator/detail/JacobianEngine.hpp
@@ -15,8 +15,7 @@
 #include "Acts/Geometry/GeometryContext.hpp"
 #include "Acts/Surfaces/Surface.hpp"
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 /// @brief These functions perform the calculation of the Jacobians for the
 /// the covariance transport. This is a purely algebraic problem the
@@ -213,5 +212,4 @@ void reinitializeJacobians(FreeMatrix& freeTransportJacobian,
                            BoundToFreeMatrix& boundToFreeJacobian,
                            const Vector3& direction);
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Propagator/detail/LoopProtection.hpp b/Core/include/Acts/Propagator/detail/LoopProtection.hpp
index c8170ce0976..1dd334a59a4 100644
--- a/Core/include/Acts/Propagator/detail/LoopProtection.hpp
+++ b/Core/include/Acts/Propagator/detail/LoopProtection.hpp
@@ -11,8 +11,7 @@
 #include "Acts/Definitions/Algebra.hpp"
 #include "Acts/Utilities/Logger.hpp"
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 /// Estimate the loop protection limit
 template <typename path_aborter_t, typename propagator_state_t,
@@ -64,5 +63,4 @@ void setupLoopProtection(propagator_state_t& state, const stepper_t& stepper,
   }
 }
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Propagator/detail/PointwiseMaterialInteraction.hpp b/Core/include/Acts/Propagator/detail/PointwiseMaterialInteraction.hpp
index 048b4d606c4..bd68a1576dd 100644
--- a/Core/include/Acts/Propagator/detail/PointwiseMaterialInteraction.hpp
+++ b/Core/include/Acts/Propagator/detail/PointwiseMaterialInteraction.hpp
@@ -21,8 +21,7 @@
 #include <algorithm>
 #include <cmath>
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 /// @brief Struct to handle pointwise material interaction
 struct PointwiseMaterialInteraction {
@@ -185,5 +184,4 @@ struct PointwiseMaterialInteraction {
                         NoiseUpdateMode updateMode = addNoise) const;
 };
 
-}  // namespace detail
-}  // end of namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Propagator/detail/SteppingHelper.hpp b/Core/include/Acts/Propagator/detail/SteppingHelper.hpp
index d2f3a7ef2f1..fcfb42b9b39 100644
--- a/Core/include/Acts/Propagator/detail/SteppingHelper.hpp
+++ b/Core/include/Acts/Propagator/detail/SteppingHelper.hpp
@@ -17,8 +17,7 @@
 #include "Acts/Utilities/Intersection.hpp"
 #include "Acts/Utilities/Logger.hpp"
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 /// Update surface status - Single component
 ///
@@ -83,5 +82,4 @@ void updateSingleStepSize(typename stepper_t::State& state,
   state.stepSize.update(stepSize, ConstrainedStep::actor, release);
 }
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Propagator/detail/VolumeMaterialInteraction.hpp b/Core/include/Acts/Propagator/detail/VolumeMaterialInteraction.hpp
index 9101843e827..8fd72f38aa8 100644
--- a/Core/include/Acts/Propagator/detail/VolumeMaterialInteraction.hpp
+++ b/Core/include/Acts/Propagator/detail/VolumeMaterialInteraction.hpp
@@ -16,8 +16,7 @@
 #include "Acts/Material/MaterialSlab.hpp"
 #include "Acts/Surfaces/Surface.hpp"
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 /// @brief Struct to handle volume material interaction
 struct VolumeMaterialInteraction {
@@ -124,5 +123,4 @@ struct VolumeMaterialInteraction {
   }
 };
 
-}  // namespace detail
-}  // end of namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Propagator/detail/abort_list_implementation.hpp b/Core/include/Acts/Propagator/detail/abort_list_implementation.hpp
index dbbccb20317..5c4a7d5b959 100644
--- a/Core/include/Acts/Propagator/detail/abort_list_implementation.hpp
+++ b/Core/include/Acts/Propagator/detail/abort_list_implementation.hpp
@@ -12,8 +12,7 @@
 
 #include <utility>
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 namespace {
 
@@ -106,5 +105,4 @@ struct abort_list_impl<> {
   }
 };
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Propagator/detail/action_list_implementation.hpp b/Core/include/Acts/Propagator/detail/action_list_implementation.hpp
index 946b69264de..c58a62191cf 100644
--- a/Core/include/Acts/Propagator/detail/action_list_implementation.hpp
+++ b/Core/include/Acts/Propagator/detail/action_list_implementation.hpp
@@ -12,8 +12,7 @@
 
 #include <utility>
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 namespace {
 
@@ -94,5 +93,4 @@ struct action_list_impl<> {
                      const navigator_t& /*navigator*/, Args&&... /*args*/) {}
 };
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Seeding/HoughTransformUtils.hpp b/Core/include/Acts/Seeding/HoughTransformUtils.hpp
index 87ae70a7d99..6b6872a74be 100644
--- a/Core/include/Acts/Seeding/HoughTransformUtils.hpp
+++ b/Core/include/Acts/Seeding/HoughTransformUtils.hpp
@@ -21,8 +21,7 @@
 
 #include "HoughVectors.hpp"
 
-namespace Acts {
-namespace HoughTransformUtils {
+namespace Acts::HoughTransformUtils {
 
 /// this type is responsible for encoding the parameters of our hough space
 using CoordType = double;
@@ -370,7 +369,6 @@ class IslandsAroundMax {
       std::make_pair(0, 1),   std::make_pair(1, 1)};
 };
 }  // namespace PeakFinders
-}  // namespace HoughTransformUtils
-}  // namespace Acts
+}  // namespace Acts::HoughTransformUtils
 
 #include "HoughTransformUtils.ipp"
diff --git a/Core/include/Acts/Seeding/InternalSpacePoint.hpp b/Core/include/Acts/Seeding/InternalSpacePoint.hpp
index e859de79ef1..6609123bf29 100644
--- a/Core/include/Acts/Seeding/InternalSpacePoint.hpp
+++ b/Core/include/Acts/Seeding/InternalSpacePoint.hpp
@@ -88,4 +88,4 @@ template <typename SpacePoint>
 inline InternalSpacePoint<SpacePoint>::InternalSpacePoint(
     const InternalSpacePoint<SpacePoint>& sp) = default;
 
-}  // end of namespace Acts
+}  // namespace Acts
diff --git a/Core/include/Acts/Surfaces/DiscSurface.hpp b/Core/include/Acts/Surfaces/DiscSurface.hpp
index fb5846af363..bb28d5f9a53 100644
--- a/Core/include/Acts/Surfaces/DiscSurface.hpp
+++ b/Core/include/Acts/Surfaces/DiscSurface.hpp
@@ -337,4 +337,4 @@ class DiscSurface : public RegularSurface {
 
 ACTS_STATIC_CHECK_CONCEPT(RegularSurfaceConcept, DiscSurface);
 
-}  // end of namespace Acts
+}  // namespace Acts
diff --git a/Core/include/Acts/Surfaces/PlaneSurface.hpp b/Core/include/Acts/Surfaces/PlaneSurface.hpp
index 90c1441f1dd..9d850b791cf 100644
--- a/Core/include/Acts/Surfaces/PlaneSurface.hpp
+++ b/Core/include/Acts/Surfaces/PlaneSurface.hpp
@@ -236,4 +236,4 @@ class PlaneSurface : public RegularSurface {
 
 ACTS_STATIC_CHECK_CONCEPT(RegularSurfaceConcept, PlaneSurface);
 
-}  // end of namespace Acts
+}  // namespace Acts
diff --git a/Core/include/Acts/Surfaces/detail/AlignmentHelper.hpp b/Core/include/Acts/Surfaces/detail/AlignmentHelper.hpp
index 2dc3721c8ab..f69de328ae1 100644
--- a/Core/include/Acts/Surfaces/detail/AlignmentHelper.hpp
+++ b/Core/include/Acts/Surfaces/detail/AlignmentHelper.hpp
@@ -14,9 +14,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-
-namespace detail {
+namespace Acts::detail {
 
 // The container for derivative of local frame axis w.r.t. its
 // rotation parameters. The first element is for x axis, second for y axis and
@@ -34,6 +32,4 @@ using RotationToAxes =
 /// rotation angles (extrinsic Euler angles) around global x/y/z axis
 RotationToAxes rotationToLocalAxesDerivative(const RotationMatrix3& rotation);
 
-}  // namespace detail
-
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Surfaces/detail/FacesHelper.hpp b/Core/include/Acts/Surfaces/detail/FacesHelper.hpp
index 7438020a268..a9eaf763db6 100644
--- a/Core/include/Acts/Surfaces/detail/FacesHelper.hpp
+++ b/Core/include/Acts/Surfaces/detail/FacesHelper.hpp
@@ -15,9 +15,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-
-namespace detail {
+namespace Acts::detail {
 
 /// @brief Helper for writing out faces for polyhedron representation
 struct FacesHelper {
@@ -83,6 +81,4 @@ struct FacesHelper {
   }
 };
 
-}  // namespace detail
-
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Surfaces/detail/IntersectionHelper2D.hpp b/Core/include/Acts/Surfaces/detail/IntersectionHelper2D.hpp
index cba67c30267..125d1fc8bc3 100644
--- a/Core/include/Acts/Surfaces/detail/IntersectionHelper2D.hpp
+++ b/Core/include/Acts/Surfaces/detail/IntersectionHelper2D.hpp
@@ -13,8 +13,7 @@
 
 #include <array>
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 struct IntersectionHelper2D {
   /// Intersect two segments
@@ -73,5 +72,4 @@ struct IntersectionHelper2D {
 
 };  // struct IntersectionHelper2D
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Surfaces/detail/PlanarHelper.hpp b/Core/include/Acts/Surfaces/detail/PlanarHelper.hpp
index 32c6a8bf75d..a83cc6563c4 100644
--- a/Core/include/Acts/Surfaces/detail/PlanarHelper.hpp
+++ b/Core/include/Acts/Surfaces/detail/PlanarHelper.hpp
@@ -11,10 +11,8 @@
 #include "Acts/Definitions/Algebra.hpp"
 #include "Acts/Utilities/Intersection.hpp"
 
-namespace Acts {
-
 /// @brief Helpers for planar surfaces that share the same maths
-namespace PlanarHelper {
+namespace Acts::PlanarHelper {
 
 /// Intersection with a planar surface
 ///
@@ -46,5 +44,4 @@ inline Intersection3D intersect(const Transform3& transform,
   return Intersection3D::invalid();
 }
 
-}  // namespace PlanarHelper
-}  // namespace Acts
+}  // namespace Acts::PlanarHelper
diff --git a/Core/include/Acts/Surfaces/detail/VerticesHelper.hpp b/Core/include/Acts/Surfaces/detail/VerticesHelper.hpp
index 3d0d0511da6..d9b06aaadd4 100644
--- a/Core/include/Acts/Surfaces/detail/VerticesHelper.hpp
+++ b/Core/include/Acts/Surfaces/detail/VerticesHelper.hpp
@@ -16,10 +16,8 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-namespace detail {
 /// Helper methods for polyhedron vertices drawing and inside/outside checks.
-namespace VerticesHelper {
+namespace Acts::detail::VerticesHelper {
 
 /// A method that inserts the cartesian extrema points and segments
 /// a curved segment into sub segments
@@ -170,6 +168,4 @@ bool isInsideRectangle(const vertex_t& point, const vertex_t& lowerLeft,
 bool onHyperPlane(const std::vector<Vector3>& vertices,
                   ActsScalar tolerance = s_onSurfaceTolerance);
 
-}  // namespace VerticesHelper
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail::VerticesHelper
diff --git a/Core/include/Acts/TrackFinding/SourceLinkAccessorConcept.hpp b/Core/include/Acts/TrackFinding/SourceLinkAccessorConcept.hpp
index 72bffeb6f8f..e20a63634cf 100644
--- a/Core/include/Acts/TrackFinding/SourceLinkAccessorConcept.hpp
+++ b/Core/include/Acts/TrackFinding/SourceLinkAccessorConcept.hpp
@@ -16,8 +16,7 @@ namespace Acts {
 
 class Surface;
 
-namespace Concepts {
-namespace SourceLinkAccessor {
+namespace Concepts::SourceLinkAccessor {
 
 template <typename T>
 using container_t = typename T::Container;
@@ -69,8 +68,7 @@ METHOD_TRAIT(at_t, at);
                                               at_exists>;
       };
 // clang-format on
-}  // namespace SourceLinkAccessor
-}  // namespace Concepts
+}  // namespace Concepts::SourceLinkAccessor
 
 template <typename accessor>
 constexpr bool SourceLinkAccessorConcept =
diff --git a/Core/include/Acts/TrackFinding/detail/AmbiguityTrackClustering.hpp b/Core/include/Acts/TrackFinding/detail/AmbiguityTrackClustering.hpp
index fb2c11f21ba..14a30bb2dd3 100644
--- a/Core/include/Acts/TrackFinding/detail/AmbiguityTrackClustering.hpp
+++ b/Core/include/Acts/TrackFinding/detail/AmbiguityTrackClustering.hpp
@@ -13,8 +13,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 /// Clusterise tracks based on shared hits
 ///
@@ -25,5 +24,4 @@ clusterDuplicateTracks(
     const std::multimap<int, std::pair<std::size_t, std::vector<std::size_t>>>&
         trackMap);
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/TrackFitting/GlobalChiSquareFitter.hpp b/Core/include/Acts/TrackFitting/GlobalChiSquareFitter.hpp
index cd446c87ef0..b7950994766 100644
--- a/Core/include/Acts/TrackFitting/GlobalChiSquareFitter.hpp
+++ b/Core/include/Acts/TrackFitting/GlobalChiSquareFitter.hpp
@@ -43,8 +43,7 @@
 #include <map>
 #include <memory>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 namespace Gx2fConstants {
 constexpr std::string_view gx2fnUpdateColumn = "Gx2fnUpdateColumn";
@@ -847,5 +846,4 @@ class Gx2Fitter {
   }
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Core/include/Acts/TrackFitting/GlobalChiSquareFitterError.hpp b/Core/include/Acts/TrackFitting/GlobalChiSquareFitterError.hpp
index 52aed8456a4..f84505769a6 100644
--- a/Core/include/Acts/TrackFitting/GlobalChiSquareFitterError.hpp
+++ b/Core/include/Acts/TrackFitting/GlobalChiSquareFitterError.hpp
@@ -11,8 +11,7 @@
 #include <system_error>
 #include <type_traits>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 enum class GlobalChiSquareFitterError {
   // ensure all values are non-zero
@@ -24,8 +23,7 @@ enum class GlobalChiSquareFitterError {
 std::error_code make_error_code(
     Acts::Experimental::GlobalChiSquareFitterError e);
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
 
 namespace std {
 // register with STL
diff --git a/Core/include/Acts/TrackFitting/detail/GsfActor.hpp b/Core/include/Acts/TrackFitting/detail/GsfActor.hpp
index 4261aebf42f..814bdeab3fb 100644
--- a/Core/include/Acts/TrackFitting/detail/GsfActor.hpp
+++ b/Core/include/Acts/TrackFitting/detail/GsfActor.hpp
@@ -29,8 +29,7 @@
 #include <map>
 #include <numeric>
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 template <typename traj_t>
 struct GsfResult {
@@ -798,5 +797,4 @@ struct GsfActor {
   }
 };
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/TrackFitting/detail/KalmanGlobalCovariance.hpp b/Core/include/Acts/TrackFitting/detail/KalmanGlobalCovariance.hpp
index 47b6dba0fc0..b5c9ded721f 100644
--- a/Core/include/Acts/TrackFitting/detail/KalmanGlobalCovariance.hpp
+++ b/Core/include/Acts/TrackFitting/detail/KalmanGlobalCovariance.hpp
@@ -17,8 +17,7 @@
 
 #include <unordered_map>
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 /// Calculate the global track parameters covariance for a smoothed trajectory
 /// stored in MultiTrajecty based on formulas at Journal of Physics: Conference
@@ -99,5 +98,4 @@ globalTrackParametersCovariance(const traj_t& multiTraj,
   return std::make_pair(fullGlobalTrackParamsCov, stateRowIndices);
 }
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/TrackFitting/detail/KalmanUpdateHelpers.hpp b/Core/include/Acts/TrackFitting/detail/KalmanUpdateHelpers.hpp
index 22d215ab93f..5b7cc8785ef 100644
--- a/Core/include/Acts/TrackFitting/detail/KalmanUpdateHelpers.hpp
+++ b/Core/include/Acts/TrackFitting/detail/KalmanUpdateHelpers.hpp
@@ -15,8 +15,7 @@
 #include "Acts/Utilities/CalibrationContext.hpp"
 #include "Acts/Utilities/Result.hpp"
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 /// This function encapsulates the Kalman update performed on a MultiTrajectory
 /// for a single source link.
@@ -190,5 +189,4 @@ auto kalmanHandleNoMeasurement(
   return trackStateProxy;
 }
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Utilities/BinnedArrayXD.hpp b/Core/include/Acts/Utilities/BinnedArrayXD.hpp
index 7bd2777da93..4b78b1026bc 100644
--- a/Core/include/Acts/Utilities/BinnedArrayXD.hpp
+++ b/Core/include/Acts/Utilities/BinnedArrayXD.hpp
@@ -196,4 +196,4 @@ class BinnedArrayXD : public BinnedArray<T> {
   /// binUtility for retrieving and filling the Array
   std::unique_ptr<const BinUtility> m_binUtility;
 };
-}  // end of namespace Acts
+}  // namespace Acts
diff --git a/Core/include/Acts/Utilities/GridAxisGenerators.hpp b/Core/include/Acts/Utilities/GridAxisGenerators.hpp
index 9aaf9cc5693..74bd488c68d 100644
--- a/Core/include/Acts/Utilities/GridAxisGenerators.hpp
+++ b/Core/include/Acts/Utilities/GridAxisGenerators.hpp
@@ -16,16 +16,13 @@
 #include <tuple>
 #include <vector>
 
-namespace Acts {
-
 /// Axis generators are used to allow defining different grid types
 /// for indexed geometry objects.
 ///
 /// The call operator() API allows to plug axis generators into
 /// dedicated code snippets and create fitting axis types on the fly
 /// which then turn into concrete Grid types.
-///
-namespace GridAxisGenerators {
+namespace Acts::GridAxisGenerators {
 
 /// @brief  Templated base generator for equidistant axis as a tuple - 1D
 ///
@@ -318,5 +315,4 @@ using PossibleAxes =
              VarOpenVarBound, VarOpenVarOpen, VarOpenVarClosed,
              VarClosedVarBound, VarClosedVarOpen, VarClosedVarClosed>;
 
-}  // namespace GridAxisGenerators
-}  // namespace Acts
+}  // namespace Acts::GridAxisGenerators
diff --git a/Core/include/Acts/Utilities/TransformRange.hpp b/Core/include/Acts/Utilities/TransformRange.hpp
index d4773cc3722..2c64fc17735 100644
--- a/Core/include/Acts/Utilities/TransformRange.hpp
+++ b/Core/include/Acts/Utilities/TransformRange.hpp
@@ -12,9 +12,7 @@
 #include <type_traits>
 #include <utility>
 
-namespace Acts {
-
-namespace detail {
+namespace Acts::detail {
 
 template <typename Callable, typename iterator_t, bool force_const>
 struct TransformRangeIterator;
@@ -224,5 +222,4 @@ struct DotGet {
   }
 };
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Utilities/VectorHelpers.hpp b/Core/include/Acts/Utilities/VectorHelpers.hpp
index cd326659511..84c0e6791da 100644
--- a/Core/include/Acts/Utilities/VectorHelpers.hpp
+++ b/Core/include/Acts/Utilities/VectorHelpers.hpp
@@ -19,8 +19,7 @@
 
 #include "Eigen/Dense"
 
-namespace Acts {
-namespace VectorHelpers {
+namespace Acts::VectorHelpers {
 
 namespace detail {
 template <class T>
@@ -235,5 +234,4 @@ inline std::pair<double, double> incidentAngles(
   return {phi, theta};
 }
 
-}  // namespace VectorHelpers
-}  // namespace Acts
+}  // namespace Acts::VectorHelpers
diff --git a/Core/include/Acts/Utilities/detail/Axis.hpp b/Core/include/Acts/Utilities/detail/Axis.hpp
index be9e22f9edd..c987e3c030b 100644
--- a/Core/include/Acts/Utilities/detail/Axis.hpp
+++ b/Core/include/Acts/Utilities/detail/Axis.hpp
@@ -15,9 +15,7 @@
 #include <cmath>
 #include <vector>
 
-namespace Acts {
-
-namespace detail {
+namespace Acts::detail {
 
 // This object can be iterated to produce up to two sequences of integer
 // indices, corresponding to the half-open integer ranges [begin1, end1[ and
@@ -660,6 +658,4 @@ class Axis<AxisType::Variable, bdt> final : public IAxis {
   /// vector of bin edges (sorted in ascending order)
   std::vector<ActsScalar> m_binEdges;
 };
-}  // namespace detail
-
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Utilities/detail/AxisFwd.hpp b/Core/include/Acts/Utilities/detail/AxisFwd.hpp
index d5d8dfa4296..72ed864d565 100644
--- a/Core/include/Acts/Utilities/detail/AxisFwd.hpp
+++ b/Core/include/Acts/Utilities/detail/AxisFwd.hpp
@@ -8,8 +8,7 @@
 
 #pragma once
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 /// Enum which determines how the axis handle its outer boundaries
 /// possible values values
 /// - Open is the default behaviour: out of bounds
@@ -40,5 +39,4 @@ class Axis;
 using EquidistantAxis = Axis<AxisType::Equidistant>;
 using VariableAxis = Axis<AxisType::Variable>;
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Utilities/detail/Extendable.hpp b/Core/include/Acts/Utilities/detail/Extendable.hpp
index ef511e76156..4ae1912b6b4 100644
--- a/Core/include/Acts/Utilities/detail/Extendable.hpp
+++ b/Core/include/Acts/Utilities/detail/Extendable.hpp
@@ -13,9 +13,7 @@
 #include <tuple>
 #include <type_traits>
 
-namespace Acts {
-
-namespace detail {
+namespace Acts::detail {
 
 /// This sctruct defines an extendable std::tuple
 ///
@@ -112,5 +110,4 @@ struct Extendable {
   std::tuple<extensions_t...> m_extensions;
 };
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Utilities/detail/MPL/all_of.hpp b/Core/include/Acts/Utilities/detail/MPL/all_of.hpp
index 87b456c6cbb..1553cb4f3f3 100644
--- a/Core/include/Acts/Utilities/detail/MPL/all_of.hpp
+++ b/Core/include/Acts/Utilities/detail/MPL/all_of.hpp
@@ -9,9 +9,7 @@
 #pragma once
 #include <type_traits>
 
-namespace Acts {
-
-namespace detail {
+namespace Acts::detail {
 
 namespace {
 // clang-format off
@@ -28,6 +26,4 @@ namespace {
 
 template <bool... values>
 constexpr bool all_of_v = all_of<values...>::value;
-}  // namespace detail
-
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Utilities/detail/MPL/any_of.hpp b/Core/include/Acts/Utilities/detail/MPL/any_of.hpp
index 313012a76f0..f56a669cfef 100644
--- a/Core/include/Acts/Utilities/detail/MPL/any_of.hpp
+++ b/Core/include/Acts/Utilities/detail/MPL/any_of.hpp
@@ -9,9 +9,7 @@
 #pragma once
 #include <type_traits>
 
-namespace Acts {
-
-namespace detail {
+namespace Acts::detail {
 
 namespace {
 // clang-format off
@@ -28,6 +26,4 @@ namespace {
 
 template <bool... values>
 constexpr bool any_of_v = any_of<values...>::value;
-}  // namespace detail
-
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Utilities/detail/MPL/are_sorted.hpp b/Core/include/Acts/Utilities/detail/MPL/are_sorted.hpp
index 4d1be61a0ea..e45cea4d3e5 100644
--- a/Core/include/Acts/Utilities/detail/MPL/are_sorted.hpp
+++ b/Core/include/Acts/Utilities/detail/MPL/are_sorted.hpp
@@ -7,9 +7,7 @@
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 #pragma once
-namespace Acts {
-/// @cond detail
-namespace detail {
+namespace Acts::detail {
 /**
  * @brief check whether integral values are sorted
  *
@@ -60,6 +58,4 @@ struct are_sorted<false, false, T, a, b, N...> {
   enum { value = (a >= b && are_sorted<false, false, T, b, N...>::value) };
 };
 /// @endcond
-}  // namespace detail
-/// @endcond
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Utilities/detail/MPL/are_within.hpp b/Core/include/Acts/Utilities/detail/MPL/are_within.hpp
index 5c0a6e072cd..ab01b96d259 100644
--- a/Core/include/Acts/Utilities/detail/MPL/are_within.hpp
+++ b/Core/include/Acts/Utilities/detail/MPL/are_within.hpp
@@ -7,9 +7,7 @@
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 #pragma once
-namespace Acts {
-/// @cond detail
-namespace detail {
+namespace Acts::detail {
 /**
  * @brief check whether integral values are within a given range
  *
@@ -44,6 +42,4 @@ struct are_within<T, MIN, MAX, a, others...> {
   };
 };
 /// @endcond
-}  // namespace detail
-/// @endcond
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Utilities/detail/MPL/at_index.hpp b/Core/include/Acts/Utilities/detail/MPL/at_index.hpp
index e45bf816a48..c1e88111bb3 100644
--- a/Core/include/Acts/Utilities/detail/MPL/at_index.hpp
+++ b/Core/include/Acts/Utilities/detail/MPL/at_index.hpp
@@ -7,9 +7,7 @@
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 #pragma once
-namespace Acts {
-/// @cond detail
-namespace detail {
+namespace Acts::detail {
 /**
  * @brief return integral constant at position in template parameter pack
  *
@@ -35,6 +33,4 @@ struct at_index<T, 0, next, others...> {
   static constexpr T value = next;
 };
 /// @endcond
-}  // namespace detail
-/// @endcond
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Utilities/detail/MPL/has_duplicates.hpp b/Core/include/Acts/Utilities/detail/MPL/has_duplicates.hpp
index 9554ce9c4b6..41b4b80d876 100644
--- a/Core/include/Acts/Utilities/detail/MPL/has_duplicates.hpp
+++ b/Core/include/Acts/Utilities/detail/MPL/has_duplicates.hpp
@@ -7,9 +7,7 @@
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 #pragma once
-namespace Acts {
-
-namespace detail {
+namespace Acts::detail {
 
 namespace {
 template <typename... Args>
@@ -43,6 +41,4 @@ struct has_duplicates<first, first, others...> {
 
 template <typename... Args>
 constexpr bool has_duplicates_v = has_duplicates<Args...>::value;
-}  // namespace detail
-
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Utilities/detail/MPL/type_collector.hpp b/Core/include/Acts/Utilities/detail/MPL/type_collector.hpp
index 42844ea8c92..3cfcf603f81 100644
--- a/Core/include/Acts/Utilities/detail/MPL/type_collector.hpp
+++ b/Core/include/Acts/Utilities/detail/MPL/type_collector.hpp
@@ -11,9 +11,7 @@
 #include <boost/hana/set.hpp>
 #include <boost/hana/type.hpp>
 
-namespace Acts {
-
-namespace detail {
+namespace Acts::detail {
 namespace hana = boost::hana;
 
 /**
@@ -105,6 +103,4 @@ constexpr bool has_action_type_v =
  */
 template <typename T>
 using action_type_t = typename action_type_extractor::extractor_impl<T>;
-}  // namespace detail
-
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Utilities/detail/RealQuadraticEquation.hpp b/Core/include/Acts/Utilities/detail/RealQuadraticEquation.hpp
index ed81028d5c3..c401d8f1549 100644
--- a/Core/include/Acts/Utilities/detail/RealQuadraticEquation.hpp
+++ b/Core/include/Acts/Utilities/detail/RealQuadraticEquation.hpp
@@ -14,8 +14,7 @@
 #include <cmath>
 #include <utility>
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 /// @struct RealQuadradicEquation
 ///   Mathematic struct for solving real quadratic equations
@@ -66,5 +65,4 @@ struct RealQuadraticEquation {
   }
 };
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Utilities/detail/Subspace.hpp b/Core/include/Acts/Utilities/detail/Subspace.hpp
index e6985c024ae..a9db25348e8 100644
--- a/Core/include/Acts/Utilities/detail/Subspace.hpp
+++ b/Core/include/Acts/Utilities/detail/Subspace.hpp
@@ -15,8 +15,7 @@
 #include <cstddef>
 #include <cstdint>
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 /// @defgroup subspace Linear subspace definitions
 ///
@@ -204,5 +203,4 @@ class FixedSizeSubspace {
 
 /// @}
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Utilities/detail/grid_helper.hpp b/Core/include/Acts/Utilities/detail/grid_helper.hpp
index c3cc2d82883..f296baaff97 100644
--- a/Core/include/Acts/Utilities/detail/grid_helper.hpp
+++ b/Core/include/Acts/Utilities/detail/grid_helper.hpp
@@ -19,9 +19,7 @@
 
 #include <boost/container/small_vector.hpp>
 
-namespace Acts {
-
-namespace detail {
+namespace Acts::detail {
 
 template <typename T>
 constexpr T ipow(T num, unsigned int pow) {
@@ -887,6 +885,4 @@ struct grid_helper {
   }
 };
 
-}  // namespace detail
-
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Utilities/detail/interpolation_impl.hpp b/Core/include/Acts/Utilities/detail/interpolation_impl.hpp
index 57890f3a1f5..9b36515421d 100644
--- a/Core/include/Acts/Utilities/detail/interpolation_impl.hpp
+++ b/Core/include/Acts/Utilities/detail/interpolation_impl.hpp
@@ -10,9 +10,7 @@
 
 #include <array>
 
-namespace Acts {
-
-namespace detail {
+namespace Acts::detail {
 
 /// @brief check types for requirements needed by interpolation
 ///
@@ -130,6 +128,4 @@ struct interpolate_impl<T, Point1, Point2, Point3, D, 2u> {
   }
 };
 /// @endcond
-}  // namespace detail
-
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/include/Acts/Utilities/detail/periodic.hpp b/Core/include/Acts/Utilities/detail/periodic.hpp
index f87454dd3bc..b9badb7a123 100644
--- a/Core/include/Acts/Utilities/detail/periodic.hpp
+++ b/Core/include/Acts/Utilities/detail/periodic.hpp
@@ -10,8 +10,7 @@
 
 #include <cmath>
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 /// Wrap a periodic value back into the nominal range.
 template <typename T>
@@ -91,5 +90,4 @@ inline std::pair<T, T> normalizePhiTheta(T phi, T theta) {
   return {radian_sym(phi), theta};
 }
 
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/src/Detector/CuboidalContainerBuilder.cpp b/Core/src/Detector/CuboidalContainerBuilder.cpp
index 7f4fb3d5696..7c403d6b55d 100644
--- a/Core/src/Detector/CuboidalContainerBuilder.cpp
+++ b/Core/src/Detector/CuboidalContainerBuilder.cpp
@@ -21,11 +21,9 @@
 #include <stdexcept>
 #include <utility>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 class DetectorVolume;
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
 
 Acts::Experimental::CuboidalContainerBuilder::CuboidalContainerBuilder(
     const Acts::Experimental::CuboidalContainerBuilder::Config& cfg,
diff --git a/Core/src/Detector/CylindricalContainerBuilder.cpp b/Core/src/Detector/CylindricalContainerBuilder.cpp
index f9b6e5d1f46..c115bcfc153 100644
--- a/Core/src/Detector/CylindricalContainerBuilder.cpp
+++ b/Core/src/Detector/CylindricalContainerBuilder.cpp
@@ -23,11 +23,9 @@
 #include <stdexcept>
 #include <utility>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 class DetectorVolume;
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
 
 namespace {
 
diff --git a/Core/src/Detector/LayerStructureBuilder.cpp b/Core/src/Detector/LayerStructureBuilder.cpp
index 968b9307a1d..09a9d923c30 100644
--- a/Core/src/Detector/LayerStructureBuilder.cpp
+++ b/Core/src/Detector/LayerStructureBuilder.cpp
@@ -31,11 +31,9 @@
 #include <stdexcept>
 #include <utility>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 class DetectorVolume;
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
 
 namespace {
 
diff --git a/Core/src/Propagator/detail/PointwiseMaterialInteraction.cpp b/Core/src/Propagator/detail/PointwiseMaterialInteraction.cpp
index e60b849edd6..8314003111e 100644
--- a/Core/src/Propagator/detail/PointwiseMaterialInteraction.cpp
+++ b/Core/src/Propagator/detail/PointwiseMaterialInteraction.cpp
@@ -10,8 +10,7 @@
 
 #include "Acts/Material/Interactions.hpp"
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 void PointwiseMaterialInteraction::evaluatePointwiseMaterialInteraction(
     bool multipleScattering, bool energyLoss) {
@@ -52,5 +51,4 @@ double PointwiseMaterialInteraction::updateVariance(
   return std::max(0., variance + std::copysign(change, updateMode));
 }
 
-}  // namespace detail
-}  // end of namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/src/TrackFitting/GsfUtils.cpp b/Core/src/TrackFitting/GsfUtils.cpp
index 02f790d261a..13043c603e2 100644
--- a/Core/src/TrackFitting/GsfUtils.cpp
+++ b/Core/src/TrackFitting/GsfUtils.cpp
@@ -12,8 +12,7 @@
 
 #include <cstddef>
 
-namespace Acts {
-namespace detail {
+namespace Acts::detail {
 
 using TrackStateTraits =
     TrackStateTraits<MultiTrajectoryTraits::MeasurementSizeMax, true>;
@@ -36,5 +35,4 @@ ActsScalar calculateDeterminant(
         .determinant();
   });
 }
-}  // namespace detail
-}  // namespace Acts
+}  // namespace Acts::detail
diff --git a/Core/src/Visualization/GeometryView3D.cpp b/Core/src/Visualization/GeometryView3D.cpp
index 0388b826da6..26710a4800a 100644
--- a/Core/src/Visualization/GeometryView3D.cpp
+++ b/Core/src/Visualization/GeometryView3D.cpp
@@ -64,15 +64,13 @@ std::string getWorkingDirectory() {
 
 }  // namespace
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 ViewConfig s_viewSensitive = ViewConfig({0, 180, 240});
 ViewConfig s_viewPassive = ViewConfig({240, 280, 0});
 ViewConfig s_viewVolume = ViewConfig({220, 220, 0});
 ViewConfig s_viewGrid = ViewConfig({220, 0, 0});
 ViewConfig s_viewLine = ViewConfig({0, 0, 220});
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
 
 void Acts::GeometryView3D::drawPolyhedron(IVisualization3D& helper,
                                           const Polyhedron& polyhedron,
diff --git a/Examples/Algorithms/Digitization/include/ActsExamples/Digitization/Smearers.hpp b/Examples/Algorithms/Digitization/include/ActsExamples/Digitization/Smearers.hpp
index a4ba5600edd..94023637068 100644
--- a/Examples/Algorithms/Digitization/include/ActsExamples/Digitization/Smearers.hpp
+++ b/Examples/Algorithms/Digitization/include/ActsExamples/Digitization/Smearers.hpp
@@ -21,8 +21,7 @@
 #include <tuple>
 #include <utility>
 
-namespace ActsExamples {
-namespace Digitization {
+namespace ActsExamples::Digitization {
 
 /// Exact smearing of a single parameter.
 ///
@@ -205,5 +204,4 @@ struct Digital {
   }
 };
 
-}  // namespace Digitization
-}  // namespace ActsExamples
+}  // namespace ActsExamples::Digitization
diff --git a/Examples/Algorithms/Geant4/include/ActsExamples/TelescopeDetector/TelescopeG4DetectorConstruction.hpp b/Examples/Algorithms/Geant4/include/ActsExamples/TelescopeDetector/TelescopeG4DetectorConstruction.hpp
index a15d73e7fea..f9cd28eae87 100644
--- a/Examples/Algorithms/Geant4/include/ActsExamples/TelescopeDetector/TelescopeG4DetectorConstruction.hpp
+++ b/Examples/Algorithms/Geant4/include/ActsExamples/TelescopeDetector/TelescopeG4DetectorConstruction.hpp
@@ -16,8 +16,7 @@
 class G4VPhysicalVolume;
 class G4LogicalVolume;
 
-namespace ActsExamples {
-namespace Telescope {
+namespace ActsExamples::Telescope {
 
 class TelescopeG4DetectorConstruction final
     : public G4VUserDetectorConstruction {
@@ -43,5 +42,4 @@ class TelescopeG4DetectorConstructionFactory final
   TelescopeDetector::Config m_cfg;
 };
 
-}  // namespace Telescope
-}  // namespace ActsExamples
+}  // namespace ActsExamples::Telescope
diff --git a/Examples/Algorithms/Geant4HepMC/src/PrimaryGeneratorAction.hpp b/Examples/Algorithms/Geant4HepMC/src/PrimaryGeneratorAction.hpp
index c6e95ca9d88..aca41fb7e37 100644
--- a/Examples/Algorithms/Geant4HepMC/src/PrimaryGeneratorAction.hpp
+++ b/Examples/Algorithms/Geant4HepMC/src/PrimaryGeneratorAction.hpp
@@ -21,9 +21,7 @@
 class G4ParticleGun;
 class G4Event;
 
-namespace ActsExamples {
-
-namespace Geant4::HepMC3 {
+namespace ActsExamples::Geant4::HepMC3 {
 
 /// The PrimaryGeneratorAction is the implementation of the Geant4
 /// class G4VUserPrimaryGeneratorAction. It generates a random direction
@@ -53,6 +51,5 @@ class PrimaryGeneratorAction : public G4VUserPrimaryGeneratorAction {
   /// The Geant4 particle table
   G4ParticleTable* m_particleTable;
 };
-}  // namespace Geant4::HepMC3
 
-}  // namespace ActsExamples
+}  // namespace ActsExamples::Geant4::HepMC3
diff --git a/Examples/Algorithms/Geometry/include/ActsExamples/Geometry/VolumeAssociationTest.hpp b/Examples/Algorithms/Geometry/include/ActsExamples/Geometry/VolumeAssociationTest.hpp
index 70cf5fa7617..897415af846 100644
--- a/Examples/Algorithms/Geometry/include/ActsExamples/Geometry/VolumeAssociationTest.hpp
+++ b/Examples/Algorithms/Geometry/include/ActsExamples/Geometry/VolumeAssociationTest.hpp
@@ -12,11 +12,9 @@
 #include "ActsExamples/Framework/ProcessCode.hpp"
 #include "ActsExamples/Framework/RandomNumbers.hpp"
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 class Detector;
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
 
 namespace ActsExamples {
 
diff --git a/Examples/Algorithms/TrackFinding/include/ActsExamples/TrackFinding/DefaultHoughFunctions.hpp b/Examples/Algorithms/TrackFinding/include/ActsExamples/TrackFinding/DefaultHoughFunctions.hpp
index 57786bea284..f158d736f61 100644
--- a/Examples/Algorithms/TrackFinding/include/ActsExamples/TrackFinding/DefaultHoughFunctions.hpp
+++ b/Examples/Algorithms/TrackFinding/include/ActsExamples/TrackFinding/DefaultHoughFunctions.hpp
@@ -24,8 +24,7 @@ template <>
 struct is_error_code_enum<HoughError> : std::true_type {};
 }  // namespace std
 
-namespace ActsExamples {
-namespace DefaultHoughFunctions {
+namespace ActsExamples::DefaultHoughFunctions {
 using ResultDouble = Acts::Result<double>;
 using ResultBool = Acts::Result<bool>;
 using ResultUnsigned = Acts::Result<unsigned>;
@@ -124,5 +123,4 @@ ResultBool inSliceDefault(double z, unsigned layer, int slice) {
     }
   }
 }
-}  // namespace DefaultHoughFunctions
-}  // namespace ActsExamples
+}  // namespace ActsExamples::DefaultHoughFunctions
diff --git a/Examples/Detectors/ContextualDetector/include/ActsExamples/ContextualDetector/AlignmentDecorator.hpp b/Examples/Detectors/ContextualDetector/include/ActsExamples/ContextualDetector/AlignmentDecorator.hpp
index 16b3af92f45..379ff8d6868 100644
--- a/Examples/Detectors/ContextualDetector/include/ActsExamples/ContextualDetector/AlignmentDecorator.hpp
+++ b/Examples/Detectors/ContextualDetector/include/ActsExamples/ContextualDetector/AlignmentDecorator.hpp
@@ -19,9 +19,7 @@
 #include <mutex>
 #include <vector>
 
-namespace ActsExamples {
-
-namespace Contextual {
+namespace ActsExamples::Contextual {
 
 /// @brief A mockup service that rotates the modules in a
 /// simple tracking geometry
@@ -87,5 +85,4 @@ class AlignmentDecorator : public IContextDecorator {
     }
   }
 };
-}  // namespace Contextual
-}  // namespace ActsExamples
+}  // namespace ActsExamples::Contextual
diff --git a/Examples/Detectors/ContextualDetector/include/ActsExamples/ContextualDetector/ExternallyAlignedDetectorElement.hpp b/Examples/Detectors/ContextualDetector/include/ActsExamples/ContextualDetector/ExternallyAlignedDetectorElement.hpp
index c7c2a56f045..a29721521d1 100644
--- a/Examples/Detectors/ContextualDetector/include/ActsExamples/ContextualDetector/ExternallyAlignedDetectorElement.hpp
+++ b/Examples/Detectors/ContextualDetector/include/ActsExamples/ContextualDetector/ExternallyAlignedDetectorElement.hpp
@@ -18,9 +18,7 @@
 
 #include <map>
 
-namespace ActsExamples {
-
-namespace Contextual {
+namespace ActsExamples::Contextual {
 
 /// @class ExternallyAlignedDetectorElement extends GenericDetectorElement
 ///
@@ -84,5 +82,4 @@ inline const Acts::Transform3& ExternallyAlignedDetectorElement::transform(
   return alignContext.alignmentStore->transforms[idValue];
 }
 
-}  // end of namespace Contextual
-}  // end of namespace ActsExamples
+}  // namespace ActsExamples::Contextual
diff --git a/Examples/Detectors/ContextualDetector/include/ActsExamples/ContextualDetector/InternallyAlignedDetectorElement.hpp b/Examples/Detectors/ContextualDetector/include/ActsExamples/ContextualDetector/InternallyAlignedDetectorElement.hpp
index a1e1908dd9c..23ac592ae98 100644
--- a/Examples/Detectors/ContextualDetector/include/ActsExamples/ContextualDetector/InternallyAlignedDetectorElement.hpp
+++ b/Examples/Detectors/ContextualDetector/include/ActsExamples/ContextualDetector/InternallyAlignedDetectorElement.hpp
@@ -21,9 +21,7 @@
 #include <mutex>
 #include <unordered_map>
 
-namespace ActsExamples {
-
-namespace Contextual {
+namespace ActsExamples::Contextual {
 
 /// @class InternallyAlignedDetectorElement extends GenericDetectorElement
 ///
@@ -121,5 +119,4 @@ inline void InternallyAlignedDetectorElement::clearAlignedTransform(
   }
 }
 
-}  // namespace Contextual
-}  // end of namespace ActsExamples
+}  // namespace ActsExamples::Contextual
diff --git a/Examples/Detectors/DD4hepDetector/include/ActsExamples/DD4hepDetector/DD4hepDetector.hpp b/Examples/Detectors/DD4hepDetector/include/ActsExamples/DD4hepDetector/DD4hepDetector.hpp
index bb2b5a3207d..bda365d6df9 100644
--- a/Examples/Detectors/DD4hepDetector/include/ActsExamples/DD4hepDetector/DD4hepDetector.hpp
+++ b/Examples/Detectors/DD4hepDetector/include/ActsExamples/DD4hepDetector/DD4hepDetector.hpp
@@ -35,8 +35,7 @@ namespace ActsExamples {
 class IContextDecorator;
 }  // namespace ActsExamples
 
-namespace ActsExamples {
-namespace DD4hep {
+namespace ActsExamples::DD4hep {
 
 struct DD4hepDetector {
   /// @brief The context decorators
@@ -93,5 +92,4 @@ struct DD4hepDetector {
   std::shared_ptr<Acts::DD4hepFieldAdapter> field() const;
 };
 
-}  // namespace DD4hep
-}  // namespace ActsExamples
+}  // namespace ActsExamples::DD4hep
diff --git a/Examples/Detectors/DD4hepDetector/include/ActsExamples/DD4hepDetector/DD4hepDetectorHelper.hpp b/Examples/Detectors/DD4hepDetector/include/ActsExamples/DD4hepDetector/DD4hepDetectorHelper.hpp
index 2bdcba266cb..69619eaf3ca 100644
--- a/Examples/Detectors/DD4hepDetector/include/ActsExamples/DD4hepDetector/DD4hepDetectorHelper.hpp
+++ b/Examples/Detectors/DD4hepDetector/include/ActsExamples/DD4hepDetector/DD4hepDetectorHelper.hpp
@@ -104,8 +104,7 @@ class DigitizationModule;
 /// created for this DetElement.
 /// @endcode
 
-namespace ActsExamples {
-namespace DD4hep {
+namespace ActsExamples::DD4hep {
 
 struct DD4hepDetectorHelper {
   /// Global method to build an Acts::DigitizationModule with rectangular
@@ -138,5 +137,4 @@ struct DD4hepDetectorHelper {
       double thickness, const dd4hep::Segmentation& segmentation);
 };
 
-}  // end of namespace DD4hep
-}  // end of namespace ActsExamples
+}  // namespace ActsExamples::DD4hep
diff --git a/Examples/Detectors/DD4hepDetector/include/ActsExamples/DD4hepDetector/DD4hepGeometryService.hpp b/Examples/Detectors/DD4hepDetector/include/ActsExamples/DD4hepDetector/DD4hepGeometryService.hpp
index 2eed6323751..25415977e2f 100644
--- a/Examples/Detectors/DD4hepDetector/include/ActsExamples/DD4hepDetector/DD4hepGeometryService.hpp
+++ b/Examples/Detectors/DD4hepDetector/include/ActsExamples/DD4hepDetector/DD4hepGeometryService.hpp
@@ -35,8 +35,7 @@ namespace dd4hep {
 class Detector;
 }  // namespace dd4hep
 
-namespace ActsExamples {
-namespace DD4hep {
+namespace ActsExamples::DD4hep {
 
 void sortFCChhDetElements(std::vector<dd4hep::DetElement>& det);
 
@@ -130,5 +129,4 @@ class DD4hepGeometryService {
   std::unique_ptr<const Acts::Logger> m_logger;
 };
 
-}  // namespace DD4hep
-}  // namespace ActsExamples
+}  // namespace ActsExamples::DD4hep
diff --git a/Examples/Detectors/DD4hepDetector/src/DD4hepDetector.cpp b/Examples/Detectors/DD4hepDetector/src/DD4hepDetector.cpp
index 6ff5172e77c..919ff0668bc 100644
--- a/Examples/Detectors/DD4hepDetector/src/DD4hepDetector.cpp
+++ b/Examples/Detectors/DD4hepDetector/src/DD4hepDetector.cpp
@@ -23,8 +23,7 @@
 #include <DD4hep/Fields.h>
 #include <boost/program_options.hpp>
 
-namespace ActsExamples {
-namespace DD4hep {
+namespace ActsExamples::DD4hep {
 
 DD4hepDetector::DD4hepDetector(
     std::shared_ptr<DD4hepGeometryService> _geometryService)
@@ -82,5 +81,4 @@ std::shared_ptr<Acts::DD4hepFieldAdapter> DD4hepDetector::field() const {
   return std::make_shared<Acts::DD4hepFieldAdapter>(detector.field());
 }
 
-}  // namespace DD4hep
-}  // namespace ActsExamples
+}  // namespace ActsExamples::DD4hep
diff --git a/Examples/Detectors/DD4hepDetector/src/DetUtils.cpp b/Examples/Detectors/DD4hepDetector/src/DetUtils.cpp
index abbad9085b5..42c2563d3d1 100644
--- a/Examples/Detectors/DD4hepDetector/src/DetUtils.cpp
+++ b/Examples/Detectors/DD4hepDetector/src/DetUtils.cpp
@@ -20,8 +20,7 @@
 #include <DD4hep/Segmentations.h>
 #include <XML/XMLTags.h>
 
-namespace det {
-namespace utils {
+namespace det::utils {
 
 std::shared_ptr<const Acts::DigitizationModule> rectangleDigiModuleXZ(
     double halflengthX, double halflengthZ, double thickness,
@@ -179,5 +178,4 @@ double getAttrValueWithFallback(const dd4hep::xml::Component& node,
     return defaultValue;
   }
 }
-}  // namespace utils
-}  // namespace det
+}  // namespace det::utils
diff --git a/Examples/Detectors/DD4hepDetector/src/DetUtils.h b/Examples/Detectors/DD4hepDetector/src/DetUtils.h
index 3b218829cd7..e29d379172c 100644
--- a/Examples/Detectors/DD4hepDetector/src/DetUtils.h
+++ b/Examples/Detectors/DD4hepDetector/src/DetUtils.h
@@ -28,8 +28,7 @@ class DigitizationModule;
  given value
  e.g. returns <layer name="2"/> when called with (detector, "layer", "name",
  "1") */
-namespace det {
-namespace utils {
+namespace det::utils {
 
 /// Global method to build an Acts::DigitizationModule with rectangular
 /// segmentation.
@@ -106,5 +105,4 @@ dd4hep::xml::Component getNodeByStrAttr(const dd4hep::xml::Handle_t& mother,
 double getAttrValueWithFallback(const dd4hep::xml::Component& node,
                                 const std::string& attrName,
                                 const double& defaultValue);
-}  // namespace utils
-}  // namespace det
+}  // namespace det::utils
diff --git a/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/BuildGenericDetector.hpp b/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/BuildGenericDetector.hpp
index cf713ba916a..bdb82d6e84b 100644
--- a/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/BuildGenericDetector.hpp
+++ b/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/BuildGenericDetector.hpp
@@ -48,8 +48,7 @@ class IMaterialDecorator;
 class ISurfaceMaterial;
 }  // namespace Acts
 
-namespace ActsExamples {
-namespace Generic {
+namespace ActsExamples::Generic {
 
 /// Helper method for positioning
 /// @param radius is the cylinder radius
@@ -835,5 +834,4 @@ std::unique_ptr<const Acts::TrackingGeometry> buildDetector(
   return trackingGeometry;
 }
 
-}  // end of namespace Generic
-}  // end of namespace ActsExamples
+}  // namespace ActsExamples::Generic
diff --git a/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/GenericDetector.hpp b/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/GenericDetector.hpp
index a7f48bf2f6e..0279b91efef 100644
--- a/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/GenericDetector.hpp
+++ b/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/GenericDetector.hpp
@@ -24,11 +24,9 @@ namespace ActsExamples {
 class IContextDecorator;
 }  // namespace ActsExamples
 
-namespace ActsExamples {
-namespace Generic {
+namespace ActsExamples::Generic {
 class GenericDetectorElement;
-}
-}  // namespace ActsExamples
+}  // namespace ActsExamples::Generic
 
 struct GenericDetector {
   using DetectorElement = ActsExamples::Generic::GenericDetectorElement;
diff --git a/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/GenericDetectorElement.hpp b/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/GenericDetectorElement.hpp
index c222c77b4ec..eadd5e59eff 100644
--- a/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/GenericDetectorElement.hpp
+++ b/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/GenericDetectorElement.hpp
@@ -25,9 +25,7 @@ class ISurfaceMaterial;
 class DigitizationModule;
 }  // namespace Acts
 
-namespace ActsExamples {
-
-namespace Generic {
+namespace ActsExamples::Generic {
 
 /// @class GenericDetectorElement
 ///
@@ -151,6 +149,4 @@ ActsExamples::Generic::GenericDetectorElement::digitizationModule() const {
   return m_digitizationModule;
 }
 
-}  // end of namespace Generic
-
-}  // end of namespace ActsExamples
+}  // namespace ActsExamples::Generic
diff --git a/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/LayerBuilderT.hpp b/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/LayerBuilderT.hpp
index 633834be53d..c317a9437e7 100644
--- a/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/LayerBuilderT.hpp
+++ b/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/LayerBuilderT.hpp
@@ -26,8 +26,7 @@
 
 #include <iostream>
 
-namespace ActsExamples {
-namespace Generic {
+namespace ActsExamples::Generic {
 
 using Acts::VectorHelpers::eta;
 using Acts::VectorHelpers::perp;
@@ -243,5 +242,4 @@ LayerBuilderT<detector_element_t>::constructEndcapLayers(
   return eLayers;
 }
 
-}  // end of namespace Generic
-}  // end of namespace ActsExamples
+}  // namespace ActsExamples::Generic
diff --git a/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/ProtoLayerCreatorT.hpp b/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/ProtoLayerCreatorT.hpp
index 257279df0dd..cc266f15c9c 100644
--- a/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/ProtoLayerCreatorT.hpp
+++ b/Examples/Detectors/GenericDetector/include/ActsExamples/GenericDetector/ProtoLayerCreatorT.hpp
@@ -35,9 +35,7 @@ class Surface;
 class DetecorElementBase;
 }  // namespace Acts
 
-namespace ActsExamples {
-
-namespace Generic {
+namespace ActsExamples::Generic {
 
 using Acts::VectorHelpers::eta;
 using Acts::VectorHelpers::perp;
@@ -579,5 +577,4 @@ ProtoLayerCreatorT<detector_element_t>::createProtoLayers(
   return epLayers;
 }
 
-}  // end of namespace Generic
-}  // end of namespace ActsExamples
+}  // namespace ActsExamples::Generic
diff --git a/Examples/Detectors/GenericDetector/src/BuildGenericDetector.cpp b/Examples/Detectors/GenericDetector/src/BuildGenericDetector.cpp
index b1c34e045d7..de056aee602 100644
--- a/Examples/Detectors/GenericDetector/src/BuildGenericDetector.cpp
+++ b/Examples/Detectors/GenericDetector/src/BuildGenericDetector.cpp
@@ -10,9 +10,7 @@
 
 #include <cmath>
 
-namespace ActsExamples {
-
-namespace Generic {
+namespace ActsExamples::Generic {
 
 /// helper method for cylinder
 std::vector<Acts::Vector3> modulePositionsCylinder(
@@ -130,6 +128,4 @@ std::vector<Acts::Vector3> modulePositionsRing(double z, double radius,
   return rPositions;
 }
 
-}  // end of namespace Generic
-
-}  // end of namespace ActsExamples
+}  // namespace ActsExamples::Generic
diff --git a/Examples/Detectors/MagneticField/include/ActsExamples/MagneticField/MagneticField.hpp b/Examples/Detectors/MagneticField/include/ActsExamples/MagneticField/MagneticField.hpp
index 65bfe27dc9e..69e5644e557 100644
--- a/Examples/Detectors/MagneticField/include/ActsExamples/MagneticField/MagneticField.hpp
+++ b/Examples/Detectors/MagneticField/include/ActsExamples/MagneticField/MagneticField.hpp
@@ -24,8 +24,7 @@
 #include <variant>
 #include <vector>
 
-namespace ActsExamples {
-namespace detail {
+namespace ActsExamples::detail {
 
 using InterpolatedMagneticField2 = Acts::InterpolatedBFieldMap<
     Acts::Grid<Acts::Vector2, Acts::detail::EquidistantAxis,
@@ -35,6 +34,4 @@ using InterpolatedMagneticField3 = Acts::InterpolatedBFieldMap<
     Acts::Grid<Acts::Vector3, Acts::detail::EquidistantAxis,
                Acts::detail::EquidistantAxis, Acts::detail::EquidistantAxis>>;
 
-}  // namespace detail
-
-}  // namespace ActsExamples
+}  // namespace ActsExamples::detail
diff --git a/Examples/Detectors/MuonSpectrometerMockupDetector/include/ActsExamples/MuonSpectrometerMockupDetector/MockupSectorBuilder.hpp b/Examples/Detectors/MuonSpectrometerMockupDetector/include/ActsExamples/MuonSpectrometerMockupDetector/MockupSectorBuilder.hpp
index 4b1e98d5a6d..8e0b37179f2 100644
--- a/Examples/Detectors/MuonSpectrometerMockupDetector/include/ActsExamples/MuonSpectrometerMockupDetector/MockupSectorBuilder.hpp
+++ b/Examples/Detectors/MuonSpectrometerMockupDetector/include/ActsExamples/MuonSpectrometerMockupDetector/MockupSectorBuilder.hpp
@@ -18,11 +18,9 @@
 
 class G4VPhysicalVolume;
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 class DetectorVolume;
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
 
 namespace ActsExamples {
 
diff --git a/Examples/Detectors/TelescopeDetector/include/ActsExamples/TelescopeDetector/BuildTelescopeDetector.hpp b/Examples/Detectors/TelescopeDetector/include/ActsExamples/TelescopeDetector/BuildTelescopeDetector.hpp
index d54a75b941d..34656cc0a32 100644
--- a/Examples/Detectors/TelescopeDetector/include/ActsExamples/TelescopeDetector/BuildTelescopeDetector.hpp
+++ b/Examples/Detectors/TelescopeDetector/include/ActsExamples/TelescopeDetector/BuildTelescopeDetector.hpp
@@ -21,8 +21,7 @@ namespace Acts {
 class TrackingGeometry;
 }  // namespace Acts
 
-namespace ActsExamples {
-namespace Telescope {
+namespace ActsExamples::Telescope {
 
 /// The telescope detector surface type
 enum class TelescopeSurfaceType {
@@ -55,5 +54,4 @@ std::unique_ptr<const Acts::TrackingGeometry> buildDetector(
     double thickness, TelescopeSurfaceType surfaceType,
     Acts::BinningValue binValue = Acts::BinningValue::binZ);
 
-}  // end of namespace Telescope
-}  // end of namespace ActsExamples
+}  // namespace ActsExamples::Telescope
diff --git a/Examples/Detectors/TelescopeDetector/include/ActsExamples/TelescopeDetector/TelescopeDetector.hpp b/Examples/Detectors/TelescopeDetector/include/ActsExamples/TelescopeDetector/TelescopeDetector.hpp
index e1d94db9604..19bb2b700d1 100644
--- a/Examples/Detectors/TelescopeDetector/include/ActsExamples/TelescopeDetector/TelescopeDetector.hpp
+++ b/Examples/Detectors/TelescopeDetector/include/ActsExamples/TelescopeDetector/TelescopeDetector.hpp
@@ -28,8 +28,7 @@ namespace ActsExamples {
 class IContextDecorator;
 }  // namespace ActsExamples
 
-namespace ActsExamples {
-namespace Telescope {
+namespace ActsExamples::Telescope {
 
 class TelescopeDetectorElement;
 class TelescopeG4DetectorConstruction;
@@ -62,5 +61,4 @@ struct TelescopeDetector {
       const std::shared_ptr<const Acts::IMaterialDecorator>& mdecorator);
 };
 
-}  // namespace Telescope
-}  // namespace ActsExamples
+}  // namespace ActsExamples::Telescope
diff --git a/Examples/Detectors/TelescopeDetector/include/ActsExamples/TelescopeDetector/TelescopeDetectorElement.hpp b/Examples/Detectors/TelescopeDetector/include/ActsExamples/TelescopeDetector/TelescopeDetectorElement.hpp
index 95af46fb643..e56bbf98465 100644
--- a/Examples/Detectors/TelescopeDetector/include/ActsExamples/TelescopeDetector/TelescopeDetectorElement.hpp
+++ b/Examples/Detectors/TelescopeDetector/include/ActsExamples/TelescopeDetector/TelescopeDetectorElement.hpp
@@ -24,8 +24,7 @@ class DiscBounds;
 class ISurfaceMaterial;
 }  // namespace Acts
 
-namespace ActsExamples {
-namespace Telescope {
+namespace ActsExamples::Telescope {
 
 /// @class TelescopeDetectorElement
 ///
@@ -160,5 +159,4 @@ TelescopeDetectorElement::alignedTransforms() const {
   return m_alignedTransforms;
 }
 
-}  // namespace Telescope
-}  // namespace ActsExamples
+}  // namespace ActsExamples::Telescope
diff --git a/Examples/Framework/include/ActsExamples/Utilities/Helpers.hpp b/Examples/Framework/include/ActsExamples/Utilities/Helpers.hpp
index 85d152c2b71..e57c650c365 100644
--- a/Examples/Framework/include/ActsExamples/Utilities/Helpers.hpp
+++ b/Examples/Framework/include/ActsExamples/Utilities/Helpers.hpp
@@ -25,9 +25,7 @@ class TH1F;
 class TH2F;
 class TProfile;
 
-namespace ActsExamples {
-
-namespace PlotHelpers {
+namespace ActsExamples::PlotHelpers {
 /// @brief Nested binning struct for booking plots
 class Binning {
  public:
@@ -145,6 +143,4 @@ TProfile* bookProf(const char* profName, const char* profTitle,
 void fillProf(TProfile* profile, float xValue, float yValue,
               float weight = 1.0);
 
-}  // namespace PlotHelpers
-
-}  // namespace ActsExamples
+}  // namespace ActsExamples::PlotHelpers
diff --git a/Examples/Framework/include/ActsExamples/Utilities/Options.hpp b/Examples/Framework/include/ActsExamples/Utilities/Options.hpp
index be291240b95..c60c3cc1812 100644
--- a/Examples/Framework/include/ActsExamples/Utilities/Options.hpp
+++ b/Examples/Framework/include/ActsExamples/Utilities/Options.hpp
@@ -14,8 +14,7 @@
 #include <optional>
 #include <vector>
 
-namespace ActsExamples {
-namespace Options {
+namespace ActsExamples::Options {
 
 /// @defgroup option-types Additional types for program options
 ///
@@ -167,5 +166,4 @@ inline std::ostream& operator<<(std::ostream& os,
   return os;
 }
 
-}  // namespace Options
-}  // namespace ActsExamples
+}  // namespace ActsExamples::Options
diff --git a/Examples/Framework/include/ActsExamples/Utilities/OptionsFwd.hpp b/Examples/Framework/include/ActsExamples/Utilities/OptionsFwd.hpp
index b97e61a34f9..945400b2922 100644
--- a/Examples/Framework/include/ActsExamples/Utilities/OptionsFwd.hpp
+++ b/Examples/Framework/include/ActsExamples/Utilities/OptionsFwd.hpp
@@ -8,16 +8,12 @@
 
 #pragma once
 
-namespace boost {
-namespace program_options {
+namespace boost::program_options {
 class options_description;
 class variables_map;
-}  // namespace program_options
-}  // namespace boost
+}  // namespace boost::program_options
 
-namespace ActsExamples {
-namespace Options {
+namespace ActsExamples::Options {
 using Description = ::boost::program_options::options_description;
 using Variables = ::boost::program_options::variables_map;
-}  // namespace Options
-}  // namespace ActsExamples
+}  // namespace ActsExamples::Options
diff --git a/Examples/Framework/include/ActsExamples/Utilities/tbbWrap.hpp b/Examples/Framework/include/ActsExamples/Utilities/tbbWrap.hpp
index 267814f0ebc..839545252c7 100644
--- a/Examples/Framework/include/ActsExamples/Utilities/tbbWrap.hpp
+++ b/Examples/Framework/include/ActsExamples/Utilities/tbbWrap.hpp
@@ -23,8 +23,6 @@
 #include <tbb/task_arena.h>
 #endif
 
-namespace ActsExamples {
-
 /// Wrapper for most of the tbb functions that we use in Sequencer.
 ///
 /// It disables the use of tbb if nthreads=1.
@@ -42,10 +40,10 @@ namespace ActsExamples {
 ///   https://stackoverflow.com/questions/59736661/how-to-completely-switch-off-threading-in-tbb-code
 
 #ifdef ACTS_EXAMPLES_NO_TBB
-namespace tbb {
+namespace ActsExamples::tbb {
 namespace task_arena {
 constexpr int automatic = -1;
-}
+}  // namespace task_arena
 
 template <typename Value>
 struct blocked_range {
@@ -57,10 +55,10 @@ struct blocked_range {
   Value my_end;
   Value my_begin;
 };
-}  // namespace tbb
+}  // namespace ActsExamples::tbb
 #endif
 
-namespace tbbWrap {
+namespace ActsExamples::tbbWrap {
 /// enableTBB keeps a record of whether we are multi-threaded (nthreads!=1) or
 /// not. This is set once in task_arena and stored globally.
 /// This means that enableTBB(nthreads) itself is not thread-safe. That should
@@ -173,5 +171,4 @@ class queuing_mutex {
   };
 };
 
-}  // namespace tbbWrap
-}  // namespace ActsExamples
+}  // namespace ActsExamples::tbbWrap
diff --git a/Examples/Framework/src/Utilities/Helpers.cpp b/Examples/Framework/src/Utilities/Helpers.cpp
index ada37f99095..544d58dfd22 100644
--- a/Examples/Framework/src/Utilities/Helpers.cpp
+++ b/Examples/Framework/src/Utilities/Helpers.cpp
@@ -18,9 +18,7 @@
 #include <TH2.h>
 #include <TProfile.h>
 
-namespace ActsExamples {
-
-namespace PlotHelpers {
+namespace ActsExamples::PlotHelpers {
 TH1F* bookHisto(const char* histName, const char* histTitle,
                 const Binning& varBinning) {
   TH1F* hist =
@@ -108,6 +106,4 @@ void fillProf(TProfile* profile, float xValue, float yValue, float weight) {
   profile->Fill(xValue, yValue, weight);
 }
 
-}  // namespace PlotHelpers
-
-}  // namespace ActsExamples
+}  // namespace ActsExamples::PlotHelpers
diff --git a/Examples/Io/EDM4hep/include/ActsExamples/Io/EDM4hep/EDM4hepUtil.hpp b/Examples/Io/EDM4hep/include/ActsExamples/Io/EDM4hep/EDM4hepUtil.hpp
index 38e12be6306..1a684e1f320 100644
--- a/Examples/Io/EDM4hep/include/ActsExamples/Io/EDM4hep/EDM4hepUtil.hpp
+++ b/Examples/Io/EDM4hep/include/ActsExamples/Io/EDM4hep/EDM4hepUtil.hpp
@@ -27,8 +27,7 @@
 #include "edm4hep/TrackerHitCollection.h"
 #include "edm4hep/TrackerHitPlane.h"
 
-namespace ActsExamples {
-namespace EDM4hepUtil {
+namespace ActsExamples::EDM4hepUtil {
 
 using MapParticleIdFrom =
     std::function<ActsFatras::Barcode(const edm4hep::MCParticle& particle)>;
@@ -138,5 +137,4 @@ uint64_t podioObjectIDToInteger(T&& o) {
   }
 }
 
-}  // namespace EDM4hepUtil
-}  // namespace ActsExamples
+}  // namespace ActsExamples::EDM4hepUtil
diff --git a/Examples/Io/HepMC3/include/ActsExamples/Io/HepMC3/HepMC3Event.hpp b/Examples/Io/HepMC3/include/ActsExamples/Io/HepMC3/HepMC3Event.hpp
index f23ae42b332..950ba814f1a 100644
--- a/Examples/Io/HepMC3/include/ActsExamples/Io/HepMC3/HepMC3Event.hpp
+++ b/Examples/Io/HepMC3/include/ActsExamples/Io/HepMC3/HepMC3Event.hpp
@@ -17,8 +17,7 @@
 #include <HepMC3/GenParticle.h>
 #include <HepMC3/GenVertex.h>
 
-namespace ActsExamples {
-namespace HepMC3Event {
+namespace ActsExamples::HepMC3Event {
 
 ///
 /// Setter
@@ -138,5 +137,4 @@ std::vector<SimParticle> beams(const HepMC3::GenEvent& event);
 /// @return List of final state particles
 std::vector<SimParticle> finalState(const HepMC3::GenEvent& event);
 
-}  // namespace HepMC3Event
-}  // namespace ActsExamples
+}  // namespace ActsExamples::HepMC3Event
diff --git a/Examples/Io/HepMC3/include/ActsExamples/Io/HepMC3/HepMC3Particle.hpp b/Examples/Io/HepMC3/include/ActsExamples/Io/HepMC3/HepMC3Particle.hpp
index c020afeaeea..1585b5f84c5 100644
--- a/Examples/Io/HepMC3/include/ActsExamples/Io/HepMC3/HepMC3Particle.hpp
+++ b/Examples/Io/HepMC3/include/ActsExamples/Io/HepMC3/HepMC3Particle.hpp
@@ -15,8 +15,7 @@
 #include <HepMC3/GenParticle.h>
 #include <HepMC3/GenVertex.h>
 
-namespace ActsExamples {
-namespace HepMC3Particle {
+namespace ActsExamples::HepMC3Particle {
 
 /// @brief Returns the barcode translated into Acts
 /// @param particle HepMC3::GenParticle particle
@@ -93,5 +92,4 @@ void energy(const std::shared_ptr<HepMC3::GenParticle>& particle,
 void mass(const std::shared_ptr<HepMC3::GenParticle>& particle,
           const double mass);
 
-}  // namespace HepMC3Particle
-}  // namespace ActsExamples
+}  // namespace ActsExamples::HepMC3Particle
diff --git a/Examples/Io/HepMC3/include/ActsExamples/Io/HepMC3/HepMC3Vertex.hpp b/Examples/Io/HepMC3/include/ActsExamples/Io/HepMC3/HepMC3Vertex.hpp
index 7ce7034a5e5..47e190b5769 100644
--- a/Examples/Io/HepMC3/include/ActsExamples/Io/HepMC3/HepMC3Vertex.hpp
+++ b/Examples/Io/HepMC3/include/ActsExamples/Io/HepMC3/HepMC3Vertex.hpp
@@ -15,8 +15,7 @@
 #include <HepMC3/GenParticle.h>
 #include <HepMC3/GenVertex.h>
 
-namespace ActsExamples {
-namespace HepMC3Vertex {
+namespace ActsExamples::HepMC3Vertex {
 
 /// @brief Returns a vertex translated into Acts
 /// @param vertex vertex in HepMC data type
@@ -92,5 +91,4 @@ void position(const std::shared_ptr<HepMC3::GenVertex>& vertex,
 /// @param time new time of the vertex
 void time(const std::shared_ptr<HepMC3::GenVertex>& vertex, double time);
 
-}  // namespace HepMC3Vertex
-}  // namespace ActsExamples
+}  // namespace ActsExamples::HepMC3Vertex
diff --git a/Examples/Io/Json/include/ActsExamples/Io/Json/JsonSurfacesReader.hpp b/Examples/Io/Json/include/ActsExamples/Io/Json/JsonSurfacesReader.hpp
index 9cac0900424..fcd16b97a8e 100644
--- a/Examples/Io/Json/include/ActsExamples/Io/Json/JsonSurfacesReader.hpp
+++ b/Examples/Io/Json/include/ActsExamples/Io/Json/JsonSurfacesReader.hpp
@@ -18,9 +18,7 @@ namespace Acts {
 class Surface;
 }
 
-namespace ActsExamples {
-
-namespace JsonSurfacesReader {
+namespace ActsExamples::JsonSurfacesReader {
 
 /// @brief Options specification for surface reading
 struct Options {
@@ -38,6 +36,4 @@ struct Options {
 Acts::GeometryHierarchyMap<std::shared_ptr<Acts::Surface>> read(
     const Options& options);
 
-}  // namespace JsonSurfacesReader
-
-}  // namespace ActsExamples
+}  // namespace ActsExamples::JsonSurfacesReader
diff --git a/Examples/Io/NuclearInteractions/include/ActsExamples/Io/NuclearInteractions/detail/NuclearInteractionParametrisation.hpp b/Examples/Io/NuclearInteractions/include/ActsExamples/Io/NuclearInteractions/detail/NuclearInteractionParametrisation.hpp
index e47749d02c6..c0efc4e1eb5 100644
--- a/Examples/Io/NuclearInteractions/include/ActsExamples/Io/NuclearInteractions/detail/NuclearInteractionParametrisation.hpp
+++ b/Examples/Io/NuclearInteractions/include/ActsExamples/Io/NuclearInteractions/detail/NuclearInteractionParametrisation.hpp
@@ -22,9 +22,7 @@
 #include <TH1F.h>
 #include <TVectorFfwd.h>
 
-namespace ActsExamples {
-namespace detail {
-namespace NuclearInteractionParametrisation {
+namespace ActsExamples::detail::NuclearInteractionParametrisation {
 
 /// This struct stores a fraction of an event around a nuclear
 /// interaction.
@@ -192,6 +190,4 @@ TVectorF softProbability(const EventCollection& events);
 /// @return The cumulative distribution for the nuclear interaction
 CumulativeDistribution cumulativeNuclearInteractionProbability(
     const EventCollection& events, unsigned int interactionProbabilityBins);
-}  // namespace NuclearInteractionParametrisation
-}  // namespace detail
-}  // namespace ActsExamples
+}  // namespace ActsExamples::detail::NuclearInteractionParametrisation
diff --git a/Examples/Io/NuclearInteractions/src/detail/NuclearInteractionParametrisation.cpp b/Examples/Io/NuclearInteractions/src/detail/NuclearInteractionParametrisation.cpp
index 446e7e1ca5e..a098b9cedcb 100644
--- a/Examples/Io/NuclearInteractions/src/detail/NuclearInteractionParametrisation.cpp
+++ b/Examples/Io/NuclearInteractions/src/detail/NuclearInteractionParametrisation.cpp
@@ -22,9 +22,7 @@
 #include <TVectorF.h>
 #include <TVectorT.h>
 
-namespace ActsExamples {
-namespace detail {
-namespace NuclearInteractionParametrisation {
+namespace ActsExamples::detail::NuclearInteractionParametrisation {
 namespace {
 
 /// @brief Evaluate the location in a standard normal distribution for a value
@@ -377,6 +375,4 @@ CumulativeDistribution cumulativeNuclearInteractionProbability(
   return histo;  // TODO: in this case the normalisation is not taking into
                  // account
 }
-}  // namespace NuclearInteractionParametrisation
-}  // namespace detail
-}  // namespace ActsExamples
+}  // namespace ActsExamples::detail::NuclearInteractionParametrisation
diff --git a/Examples/Io/Root/include/ActsExamples/Io/Root/RootUtility.hpp b/Examples/Io/Root/include/ActsExamples/Io/Root/RootUtility.hpp
index 892d11bdfaa..addbcc7a583 100644
--- a/Examples/Io/Root/include/ActsExamples/Io/Root/RootUtility.hpp
+++ b/Examples/Io/Root/include/ActsExamples/Io/Root/RootUtility.hpp
@@ -12,8 +12,7 @@
 
 #include <TMathBase.h>
 
-namespace ActsExamples {
-namespace RootUtility {
+namespace ActsExamples::RootUtility {
 
 /// @brief Sorts an array of elements and outputs the indices of the sorted elements.
 ///
@@ -53,5 +52,4 @@ void stableSort(index_t numElements, const element_t* elements,
   }
 }
 
-}  // namespace RootUtility
-}  // namespace ActsExamples
+}  // namespace ActsExamples::RootUtility
diff --git a/Examples/Python/src/ExaTrkXTrackFindingStub.cpp b/Examples/Python/src/ExaTrkXTrackFindingStub.cpp
index 7fa15ed37fb..00275ef1bea 100644
--- a/Examples/Python/src/ExaTrkXTrackFindingStub.cpp
+++ b/Examples/Python/src/ExaTrkXTrackFindingStub.cpp
@@ -6,11 +6,9 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-namespace Acts {
-namespace Python {
+namespace Acts::Python {
 struct Context;
-}  // namespace Python
-}  // namespace Acts
+}  // namespace Acts::Python
 
 namespace Acts::Python {
 void addExaTrkXTrackFinding(Context& /*ctx*/) {
diff --git a/Examples/Python/src/HepMC3Stub.cpp b/Examples/Python/src/HepMC3Stub.cpp
index 448436a874d..7e3919d9dca 100644
--- a/Examples/Python/src/HepMC3Stub.cpp
+++ b/Examples/Python/src/HepMC3Stub.cpp
@@ -6,11 +6,9 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-namespace Acts {
-namespace Python {
+namespace Acts::Python {
 struct Context;
-}  // namespace Python
-}  // namespace Acts
+}  // namespace Acts::Python
 
 namespace Acts::Python {
 void addHepMC3(Context& /*ctx*/) {}
diff --git a/Examples/Python/src/OnnxStub.cpp b/Examples/Python/src/OnnxStub.cpp
index 3785307347e..3c070e417d6 100644
--- a/Examples/Python/src/OnnxStub.cpp
+++ b/Examples/Python/src/OnnxStub.cpp
@@ -6,11 +6,9 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-namespace Acts {
-namespace Python {
+namespace Acts::Python {
 struct Context;
-}  // namespace Python
-}  // namespace Acts
+}  // namespace Acts::Python
 
 namespace Acts::Python {
 void addOnnx(Context& /*unused*/) {
diff --git a/Examples/Python/src/SvgStub.cpp b/Examples/Python/src/SvgStub.cpp
index d53232af188..61bce57b319 100644
--- a/Examples/Python/src/SvgStub.cpp
+++ b/Examples/Python/src/SvgStub.cpp
@@ -6,11 +6,9 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-namespace Acts {
-namespace Python {
+namespace Acts::Python {
 struct Context;
-}  // namespace Python
-}  // namespace Acts
+}  // namespace Acts::Python
 
 namespace Acts::Python {
 void addSvg(Context& /*ctx*/) {}
diff --git a/Fatras/include/ActsFatras/Kernel/detail/SimulationActor.hpp b/Fatras/include/ActsFatras/Kernel/detail/SimulationActor.hpp
index 82f532cad84..88edd988013 100644
--- a/Fatras/include/ActsFatras/Kernel/detail/SimulationActor.hpp
+++ b/Fatras/include/ActsFatras/Kernel/detail/SimulationActor.hpp
@@ -22,8 +22,7 @@
 #include <cmath>
 #include <limits>
 
-namespace ActsFatras {
-namespace detail {
+namespace ActsFatras::detail {
 
 /// Fatras simulation actor for the Acts propagator.
 ///
@@ -353,5 +352,4 @@ struct SimulationActor {
   }
 };
 
-}  // namespace detail
-}  // namespace ActsFatras
+}  // namespace ActsFatras::detail
diff --git a/Fatras/include/ActsFatras/Kernel/detail/SimulationError.hpp b/Fatras/include/ActsFatras/Kernel/detail/SimulationError.hpp
index b9478dc69b0..56b3c6bc515 100644
--- a/Fatras/include/ActsFatras/Kernel/detail/SimulationError.hpp
+++ b/Fatras/include/ActsFatras/Kernel/detail/SimulationError.hpp
@@ -11,8 +11,7 @@
 #include <system_error>
 #include <type_traits>
 
-namespace ActsFatras {
-namespace detail {
+namespace ActsFatras::detail {
 
 enum class SimulationError {
   // ensure all values are non-zero
@@ -24,8 +23,7 @@ enum class SimulationError {
 /// Must use snake_case naming for STL compatibility.
 std::error_code make_error_code(SimulationError e);
 
-}  // namespace detail
-}  // namespace ActsFatras
+}  // namespace ActsFatras::detail
 
 // Register the error enum as STL-compatible.
 namespace std {
diff --git a/Fatras/include/ActsFatras/Physics/ElectroMagnetic/detail/GaussianMixture.hpp b/Fatras/include/ActsFatras/Physics/ElectroMagnetic/detail/GaussianMixture.hpp
index 1a9d2f1799e..70274e11c40 100644
--- a/Fatras/include/ActsFatras/Physics/ElectroMagnetic/detail/GaussianMixture.hpp
+++ b/Fatras/include/ActsFatras/Physics/ElectroMagnetic/detail/GaussianMixture.hpp
@@ -12,8 +12,7 @@
 
 #include <random>
 
-namespace ActsFatras {
-namespace detail {
+namespace ActsFatras::detail {
 
 /// Generate scattering angles using a Gaussian mixture model.
 struct GaussianMixture {
@@ -89,5 +88,4 @@ struct GaussianMixture {
   }
 };
 
-}  // namespace detail
-}  // namespace ActsFatras
+}  // namespace ActsFatras::detail
diff --git a/Fatras/include/ActsFatras/Physics/ElectroMagnetic/detail/GeneralMixture.hpp b/Fatras/include/ActsFatras/Physics/ElectroMagnetic/detail/GeneralMixture.hpp
index 99101f61333..200e84bc1f7 100644
--- a/Fatras/include/ActsFatras/Physics/ElectroMagnetic/detail/GeneralMixture.hpp
+++ b/Fatras/include/ActsFatras/Physics/ElectroMagnetic/detail/GeneralMixture.hpp
@@ -13,8 +13,7 @@
 
 #include <random>
 
-namespace ActsFatras {
-namespace detail {
+namespace ActsFatras::detail {
 
 /// Generate scattering angles using a general mixture model.
 ///
@@ -201,5 +200,4 @@ struct GeneralMixture {
   }
 };
 
-}  // namespace detail
-}  // namespace ActsFatras
+}  // namespace ActsFatras::detail
diff --git a/Fatras/include/ActsFatras/Physics/ElectroMagnetic/detail/Highland.hpp b/Fatras/include/ActsFatras/Physics/ElectroMagnetic/detail/Highland.hpp
index e7a9110f277..5ac710ed727 100644
--- a/Fatras/include/ActsFatras/Physics/ElectroMagnetic/detail/Highland.hpp
+++ b/Fatras/include/ActsFatras/Physics/ElectroMagnetic/detail/Highland.hpp
@@ -12,8 +12,7 @@
 
 #include <random>
 
-namespace ActsFatras {
-namespace detail {
+namespace ActsFatras::detail {
 
 /// Generate scattering angles using the Highland/PDG parametrization.
 ///
@@ -40,5 +39,4 @@ struct Highland {
   }
 };
 
-}  // namespace detail
-}  // namespace ActsFatras
+}  // namespace ActsFatras::detail
diff --git a/Fatras/include/ActsFatras/Physics/NuclearInteraction/NuclearInteractionParameters.hpp b/Fatras/include/ActsFatras/Physics/NuclearInteraction/NuclearInteractionParameters.hpp
index 82dc5a3d847..2621c4d8b5f 100644
--- a/Fatras/include/ActsFatras/Physics/NuclearInteraction/NuclearInteractionParameters.hpp
+++ b/Fatras/include/ActsFatras/Physics/NuclearInteraction/NuclearInteractionParameters.hpp
@@ -12,8 +12,7 @@
 
 #include <vector>
 
-namespace ActsFatras {
-namespace detail {
+namespace ActsFatras::detail {
 
 /// @brief Data storage of the parametrized nuclear interaction
 struct NuclearInteractionParameters {
@@ -104,5 +103,4 @@ using NuclearInteractionParametrisation =
 /// Parametrisation of multiple particles
 using MultiParticleNuclearInteractionParametrisation =
     std::vector<std::pair<int, NuclearInteractionParametrisation>>;
-}  // namespace detail
-}  // namespace ActsFatras
+}  // namespace ActsFatras::detail
diff --git a/Fatras/include/ActsFatras/Selectors/KinematicCasts.hpp b/Fatras/include/ActsFatras/Selectors/KinematicCasts.hpp
index 045e7691259..56305f3ca2e 100644
--- a/Fatras/include/ActsFatras/Selectors/KinematicCasts.hpp
+++ b/Fatras/include/ActsFatras/Selectors/KinematicCasts.hpp
@@ -13,8 +13,7 @@
 
 #include <cmath>
 
-namespace ActsFatras {
-namespace Casts {
+namespace ActsFatras::Casts {
 
 /// Retrieve the transverse absolute distance of the position to the origin.
 struct Vrho {
@@ -76,5 +75,4 @@ struct E {
   }
 };
 
-}  // namespace Casts
-}  // namespace ActsFatras
+}  // namespace ActsFatras::Casts
diff --git a/Fatras/include/ActsFatras/Selectors/detail/combine_selectors.hpp b/Fatras/include/ActsFatras/Selectors/detail/combine_selectors.hpp
index 15f2bad4d7e..23a95492c62 100644
--- a/Fatras/include/ActsFatras/Selectors/detail/combine_selectors.hpp
+++ b/Fatras/include/ActsFatras/Selectors/detail/combine_selectors.hpp
@@ -12,8 +12,7 @@
 #include <type_traits>
 #include <utility>
 
-namespace ActsFatras {
-namespace detail {
+namespace ActsFatras::detail {
 
 /// Combine multiple selectors with a configurable combine function.
 template <bool Initial, typename Combine, typename... Selectors>
@@ -65,5 +64,4 @@ class CombineSelectors {
   }
 };
 
-}  // namespace detail
-}  // namespace ActsFatras
+}  // namespace ActsFatras::detail
diff --git a/Fatras/src/Kernel/SimulationError.cpp b/Fatras/src/Kernel/SimulationError.cpp
index 029e7eaa7e6..7c86bcc7890 100644
--- a/Fatras/src/Kernel/SimulationError.cpp
+++ b/Fatras/src/Kernel/SimulationError.cpp
@@ -10,8 +10,7 @@
 
 #include <string>
 
-namespace ActsFatras {
-namespace detail {
+namespace ActsFatras::detail {
 namespace {
 
 // Define a custom error code category derived from std::error_category
@@ -36,5 +35,4 @@ std::error_code make_error_code(SimulationError e) {
   return {static_cast<int>(e), s_simulatorErrorCategory};
 }
 
-}  // namespace detail
-}  // namespace ActsFatras
+}  // namespace ActsFatras::detail
diff --git a/Plugins/DD4hep/include/Acts/Plugins/DD4hep/DD4hepBlueprintFactory.hpp b/Plugins/DD4hep/include/Acts/Plugins/DD4hep/DD4hepBlueprintFactory.hpp
index ff9b84612b9..0f89983507c 100644
--- a/Plugins/DD4hep/include/Acts/Plugins/DD4hep/DD4hepBlueprintFactory.hpp
+++ b/Plugins/DD4hep/include/Acts/Plugins/DD4hep/DD4hepBlueprintFactory.hpp
@@ -28,8 +28,7 @@
 #include <DD4hep/DD4hepUnits.h>
 #include <DD4hep/DetElement.h>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 class DD4hepBlueprintFactory {
  public:
@@ -133,5 +132,4 @@ class DD4hepBlueprintFactory {
                    const std::string& baseName) const;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Plugins/DD4hep/include/Acts/Plugins/DD4hep/DD4hepDetectorStructure.hpp b/Plugins/DD4hep/include/Acts/Plugins/DD4hep/DD4hepDetectorStructure.hpp
index abb482cc7fc..47fbf866d14 100644
--- a/Plugins/DD4hep/include/Acts/Plugins/DD4hep/DD4hepDetectorStructure.hpp
+++ b/Plugins/DD4hep/include/Acts/Plugins/DD4hep/DD4hepDetectorStructure.hpp
@@ -22,9 +22,7 @@ namespace dd4hep {
 class DetElement;
 }
 
-namespace Acts {
-
-namespace Experimental {
+namespace Acts::Experimental {
 
 /// @brief This class allows to generate layer structure builders for dd4hep sub detectors
 /// It performs an intermediate step by taking dd4hep::DetElemnent objects that
@@ -81,5 +79,4 @@ class DD4hepDetectorStructure {
   const Logger& logger() const { return *m_logger; }
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Plugins/DD4hep/include/Acts/Plugins/DD4hep/DD4hepLayerStructure.hpp b/Plugins/DD4hep/include/Acts/Plugins/DD4hep/DD4hepLayerStructure.hpp
index ab7685cf064..441386857b2 100644
--- a/Plugins/DD4hep/include/Acts/Plugins/DD4hep/DD4hepLayerStructure.hpp
+++ b/Plugins/DD4hep/include/Acts/Plugins/DD4hep/DD4hepLayerStructure.hpp
@@ -26,9 +26,7 @@ namespace dd4hep {
 class DetElement;
 }
 
-namespace Acts {
-
-namespace Experimental {
+namespace Acts::Experimental {
 
 /// @brief This class allows to generate layer structure builders for dd4hep sub detectors
 /// It performs an intermediate step by taking dd4hep::DetElemnent objects that
@@ -103,5 +101,4 @@ class DD4hepLayerStructure {
   const Logger& logger() const { return *m_logger; }
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Plugins/DD4hep/src/ConvertDD4hepDetector.cpp b/Plugins/DD4hep/src/ConvertDD4hepDetector.cpp
index f77d60389b5..7fd18a0532f 100644
--- a/Plugins/DD4hep/src/ConvertDD4hepDetector.cpp
+++ b/Plugins/DD4hep/src/ConvertDD4hepDetector.cpp
@@ -634,4 +634,4 @@ void collectLayers_dd4hep(dd4hep::DetElement& detElement,
   }
 }
 
-}  // End of namespace Acts
+}  // namespace Acts
diff --git a/Plugins/EDM4hep/include/Acts/Plugins/EDM4hep/EDM4hepUtil.hpp b/Plugins/EDM4hep/include/Acts/Plugins/EDM4hep/EDM4hepUtil.hpp
index 1b31bfa8e37..505f9bbe1cc 100644
--- a/Plugins/EDM4hep/include/Acts/Plugins/EDM4hep/EDM4hepUtil.hpp
+++ b/Plugins/EDM4hep/include/Acts/Plugins/EDM4hep/EDM4hepUtil.hpp
@@ -30,8 +30,7 @@
 
 #include "edm4hep/MutableTrack.h"
 
-namespace Acts {
-namespace EDM4hepUtil {
+namespace Acts::EDM4hepUtil {
 
 static constexpr std::int32_t EDM4HEP_ACTS_POSITION_TYPE = 42;
 
@@ -248,5 +247,4 @@ void readTrack(const edm4hep::Track& from,
   track.nMeasurements() = track.nTrackStates();
 }
 
-}  // namespace EDM4hepUtil
-}  // namespace Acts
+}  // namespace Acts::EDM4hepUtil
diff --git a/Plugins/EDM4hep/src/EDM4hepUtil.cpp b/Plugins/EDM4hep/src/EDM4hepUtil.cpp
index 3bdc7f9677e..ec22eb9c1a2 100644
--- a/Plugins/EDM4hep/src/EDM4hepUtil.cpp
+++ b/Plugins/EDM4hep/src/EDM4hepUtil.cpp
@@ -18,9 +18,7 @@
 
 #include "edm4hep/TrackState.h"
 
-namespace Acts {
-namespace EDM4hepUtil {
-namespace detail {
+namespace Acts::EDM4hepUtil::detail {
 
 ActsSquareMatrix<6> jacobianToEdm4hep(double theta, double qOverP, double Bz) {
   // Calculate jacobian from our internal parametrization (d0, z0, phi, theta,
@@ -184,6 +182,4 @@ BoundTrackParameters convertTrackParametersFromEdm4hep(
   return {params.surface, targetPars, cov, params.particleHypothesis};
 }
 
-}  // namespace detail
-}  // namespace EDM4hepUtil
-}  // namespace Acts
+}  // namespace Acts::EDM4hepUtil::detail
diff --git a/Plugins/Geant4/include/Acts/Plugins/Geant4/Geant4SurfaceProvider.hpp b/Plugins/Geant4/include/Acts/Plugins/Geant4/Geant4SurfaceProvider.hpp
index 268d2089205..7747cce104a 100644
--- a/Plugins/Geant4/include/Acts/Plugins/Geant4/Geant4SurfaceProvider.hpp
+++ b/Plugins/Geant4/include/Acts/Plugins/Geant4/Geant4SurfaceProvider.hpp
@@ -16,8 +16,7 @@
 #include "G4LogicalVolume.hh"
 #include "G4VPhysicalVolume.hh"
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 /// @brief A surface provider that extracts surfaces from a gdml file
 ///
@@ -157,5 +156,4 @@ class Geant4SurfaceProvider : public Acts::Experimental::ISurfacesProvider {
   G4Transform3D m_g4ToWorld;
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
diff --git a/Plugins/Identification/include/Acts/Plugins/Identification/IdentifiedDetectorElement.hpp b/Plugins/Identification/include/Acts/Plugins/Identification/IdentifiedDetectorElement.hpp
index 47802a04af0..60d7e9cb87d 100644
--- a/Plugins/Identification/include/Acts/Plugins/Identification/IdentifiedDetectorElement.hpp
+++ b/Plugins/Identification/include/Acts/Plugins/Identification/IdentifiedDetectorElement.hpp
@@ -37,4 +37,4 @@ class IdentifiedDetectorElement : public DetectorElementBase {
       const = 0;
 };
 
-}  // end of namespace Acts
+}  // namespace Acts
diff --git a/Plugins/Json/include/Acts/Plugins/Json/DetectorVolumeFinderJsonConverter.hpp b/Plugins/Json/include/Acts/Plugins/Json/DetectorVolumeFinderJsonConverter.hpp
index c48c7aea327..67206b9a2c4 100644
--- a/Plugins/Json/include/Acts/Plugins/Json/DetectorVolumeFinderJsonConverter.hpp
+++ b/Plugins/Json/include/Acts/Plugins/Json/DetectorVolumeFinderJsonConverter.hpp
@@ -17,9 +17,7 @@
 
 #include <vector>
 
-namespace Acts {
-
-namespace DetectorVolumeFinderJsonConverter {
+namespace Acts::DetectorVolumeFinderJsonConverter {
 
 /// @brief Convert the single delegate if it is of the type of the reference
 ///
@@ -98,5 +96,4 @@ static inline nlohmann::json toJson(
 Experimental::DetectorVolumeUpdater fromJson(
     const nlohmann::json& jVolumeFinder);
 
-}  // namespace DetectorVolumeFinderJsonConverter
-}  // namespace Acts
+}  // namespace Acts::DetectorVolumeFinderJsonConverter
diff --git a/Plugins/Json/include/Acts/Plugins/Json/DetrayJsonHelper.hpp b/Plugins/Json/include/Acts/Plugins/Json/DetrayJsonHelper.hpp
index 421362e0137..84519166324 100644
--- a/Plugins/Json/include/Acts/Plugins/Json/DetrayJsonHelper.hpp
+++ b/Plugins/Json/include/Acts/Plugins/Json/DetrayJsonHelper.hpp
@@ -16,9 +16,7 @@
 
 #include <nlohmann/json.hpp>
 
-namespace Acts {
-
-namespace DetrayJsonHelper {
+namespace Acts::DetrayJsonHelper {
 
 /// @brief Helper function to switch keys from ACTS to detray
 ///
@@ -130,5 +128,4 @@ inline static std::size_t accelerationLink(const binning_values_t& casts) {
   return accLink;
 }
 
-}  // namespace DetrayJsonHelper
-}  // namespace Acts
+}  // namespace Acts::DetrayJsonHelper
diff --git a/Plugins/Legacy/include/Acts/Seeding/AtlasSeedFinder.hpp b/Plugins/Legacy/include/Acts/Seeding/AtlasSeedFinder.hpp
index a5d6569f56e..706d0823f2d 100644
--- a/Plugins/Legacy/include/Acts/Seeding/AtlasSeedFinder.hpp
+++ b/Plugins/Legacy/include/Acts/Seeding/AtlasSeedFinder.hpp
@@ -21,8 +21,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-namespace Legacy {
+namespace Acts::Legacy {
 template <typename SpacePoint>
 class AtlasSeedFinder {
   struct Config {
@@ -351,6 +350,5 @@ class comCurvature {
     return i1.first < i2.first;
   }
 };
-}  // namespace Legacy
-}  // namespace Acts
+}  // namespace Acts::Legacy
 #include "Acts/Seeding/AtlasSeedFinder.ipp"
diff --git a/Plugins/Legacy/include/Acts/Seeding/LegacyInternalSeed.hpp b/Plugins/Legacy/include/Acts/Seeding/LegacyInternalSeed.hpp
index 041685e998e..8698987865d 100644
--- a/Plugins/Legacy/include/Acts/Seeding/LegacyInternalSeed.hpp
+++ b/Plugins/Legacy/include/Acts/Seeding/LegacyInternalSeed.hpp
@@ -14,8 +14,7 @@
 #include "Acts/Seeding/LegacySeed.hpp"
 #include "Acts/Seeding/SPForSeed.hpp"
 
-namespace Acts {
-namespace Legacy {
+namespace Acts::Legacy {
 template <typename SpacePoint>
 class InternalSeed {
   /////////////////////////////////////////////////////////////////////////////////
@@ -170,5 +169,4 @@ inline bool InternalSeed<SpacePoint>::setQuality(float q) {
 
 /// @endcond
 
-}  // namespace Legacy
-}  // namespace Acts
+}  // namespace Acts::Legacy
diff --git a/Plugins/Legacy/include/Acts/Seeding/LegacySeed.hpp b/Plugins/Legacy/include/Acts/Seeding/LegacySeed.hpp
index 527b18a3a2f..45f9406083b 100644
--- a/Plugins/Legacy/include/Acts/Seeding/LegacySeed.hpp
+++ b/Plugins/Legacy/include/Acts/Seeding/LegacySeed.hpp
@@ -13,8 +13,7 @@
 #pragma once
 #include <list>
 
-namespace Acts {
-namespace Legacy {
+namespace Acts::Legacy {
 
 template <typename SpacePoint>
 class Seed {
@@ -110,5 +109,4 @@ Seed<SpacePoint>::~Seed() = default;
 
 /// @endcond
 
-}  // namespace Legacy
-}  // namespace Acts
+}  // namespace Acts::Legacy
diff --git a/Plugins/Legacy/include/Acts/Seeding/SPForSeed.hpp b/Plugins/Legacy/include/Acts/Seeding/SPForSeed.hpp
index 4c889ad6746..fc4d3ac435c 100644
--- a/Plugins/Legacy/include/Acts/Seeding/SPForSeed.hpp
+++ b/Plugins/Legacy/include/Acts/Seeding/SPForSeed.hpp
@@ -28,8 +28,7 @@
 //    if(de->isBarrel()) {m_covz = 8.*f22; m_covr = .1;}
 //    else               {m_covr = 8.*f22; m_covz = .1;}
 
-namespace Acts {
-namespace Legacy {
+namespace Acts::Legacy {
 
 template <typename SpacePoint>
 class SPForSeed {
@@ -247,5 +246,4 @@ inline void SPForSeed<SpacePoint>::setQuality(float q) {
   }
 }
 
-}  // namespace Legacy
-}  // namespace Acts
+}  // namespace Acts::Legacy
diff --git a/Tests/Benchmarks/SurfaceIntersectionBenchmark.cpp b/Tests/Benchmarks/SurfaceIntersectionBenchmark.cpp
index 28791a1bf15..392e5367995 100644
--- a/Tests/Benchmarks/SurfaceIntersectionBenchmark.cpp
+++ b/Tests/Benchmarks/SurfaceIntersectionBenchmark.cpp
@@ -27,8 +27,7 @@
 namespace bdata = boost::unit_test::data;
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Some randomness & number crunching
 unsigned int ntests = 10;
@@ -123,5 +122,4 @@ BOOST_DATA_TEST_CASE(
   }
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/BenchmarkTools.hpp b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/BenchmarkTools.hpp
index dbceeb05640..a53eba2f3f0 100644
--- a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/BenchmarkTools.hpp
+++ b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/BenchmarkTools.hpp
@@ -21,8 +21,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // === INTRODUCTION ===
 //
@@ -553,5 +552,4 @@ MicroBenchmarkResult microBenchmark(
       inputs.size(), num_runs, warmup_time);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/CubicTrackingGeometry.hpp b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/CubicTrackingGeometry.hpp
index 4dfdc816ac2..7a24126db56 100644
--- a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/CubicTrackingGeometry.hpp
+++ b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/CubicTrackingGeometry.hpp
@@ -33,8 +33,7 @@
 #include <functional>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 struct CubicTrackingGeometry {
   /// Default constructor for the Cubic tracking geometry
@@ -202,5 +201,4 @@ struct CubicTrackingGeometry {
 
   std::reference_wrapper<const GeometryContext> geoContext;
 };
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/CylindricalTrackingGeometry.hpp b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/CylindricalTrackingGeometry.hpp
index e5a8fd1d49f..c6491a2a46f 100644
--- a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/CylindricalTrackingGeometry.hpp
+++ b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/CylindricalTrackingGeometry.hpp
@@ -38,8 +38,7 @@
 #include <functional>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 struct CylindricalTrackingGeometry {
   std::reference_wrapper<const GeometryContext> geoContext;
@@ -334,5 +333,4 @@ struct CylindricalTrackingGeometry {
   }
 };
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/DataDirectory.hpp b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/DataDirectory.hpp
index 4bcb95e4b8d..378abb4f697 100644
--- a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/DataDirectory.hpp
+++ b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/DataDirectory.hpp
@@ -10,13 +10,11 @@
 
 #include <string>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 /// Get the full path to a file in the test data directory.
 ///
 /// @param relativePath file path relative to the data directory
 std::string getDataPath(const std::string& relativePath);
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/FloatComparisons.hpp b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/FloatComparisons.hpp
index 60fc71a3eb7..e6b9550e728 100644
--- a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/FloatComparisons.hpp
+++ b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/FloatComparisons.hpp
@@ -56,8 +56,7 @@
 
 // The relevant infrastructure is implemented below
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 namespace float_compare_internal {
 
 // Under the hood, various scalar comparison logics may be used
@@ -307,5 +306,4 @@ boost::test_tools::predicate_result checkCloseCovariance(
   }
   return true;
 }
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/LineSurfaceStub.hpp b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/LineSurfaceStub.hpp
index 3366cee816c..4070074539c 100644
--- a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/LineSurfaceStub.hpp
+++ b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/LineSurfaceStub.hpp
@@ -12,8 +12,7 @@
 
 #include <limits>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 class LineSurfaceStub : public LineSurface {
  public:
@@ -66,5 +65,4 @@ class LineSurfaceStub : public LineSurface {
     return Polyhedron({}, {}, {});
   }
 };
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/MeasurementsCreator.hpp b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/MeasurementsCreator.hpp
index 9a20f419cdd..35bab1eaac1 100644
--- a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/MeasurementsCreator.hpp
+++ b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/MeasurementsCreator.hpp
@@ -23,8 +23,7 @@
 #include <random>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 /// All supported simulated measurement types.
 enum class MeasurementType {
@@ -172,5 +171,4 @@ Measurements createMeasurements(const propagator_t& propagator,
   return std::move(result.template get<Measurements>());
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/PredefinedMaterials.hpp b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/PredefinedMaterials.hpp
index 2898dd943bd..4ddf0a7e66d 100644
--- a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/PredefinedMaterials.hpp
+++ b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/PredefinedMaterials.hpp
@@ -15,8 +15,7 @@
 #include "Acts/Material/Material.hpp"
 #include "Acts/Material/MaterialSlab.hpp"
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 inline Material makeBeryllium() {
   using namespace UnitLiterals;
@@ -46,5 +45,4 @@ inline MaterialSlab makePercentSlab() {
   return slab;
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestSpacePoint.hpp b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestSpacePoint.hpp
index be517a3701a..aec14a5d0f8 100644
--- a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestSpacePoint.hpp
+++ b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestSpacePoint.hpp
@@ -18,8 +18,7 @@
 
 #include <boost/container/static_vector.hpp>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 /// Space point representation of a measurement suitable for track seeding.
 class TestSpacePoint {
@@ -97,5 +96,4 @@ inline bool operator==(const TestSpacePoint& lhs, const TestSpacePoint& rhs) {
 /// Container of space points.
 using TestSpacePointContainer = std::vector<TestSpacePoint>;
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/IntegrationTests/InterpolatedSolenoidBFieldTest.cpp b/Tests/IntegrationTests/InterpolatedSolenoidBFieldTest.cpp
index 672a31c5bdc..86276a36758 100644
--- a/Tests/IntegrationTests/InterpolatedSolenoidBFieldTest.cpp
+++ b/Tests/IntegrationTests/InterpolatedSolenoidBFieldTest.cpp
@@ -26,8 +26,7 @@ using namespace Acts::UnitLiterals;
 
 namespace bdata = boost::unit_test::data;
 
-namespace Acts {
-namespace IntegrationTest {
+namespace Acts::IntegrationTest {
 
 const double L = 5.8_m;
 const double R = (2.56 + 2.46) * 0.5 * 0.5_m;
@@ -129,5 +128,4 @@ BOOST_DATA_TEST_CASE(
   ofstr << Bm.x() << ";" << Bm.y() << ";" << Bm.z() << std::endl;
 }
 
-}  // namespace IntegrationTest
-}  // namespace Acts
+}  // namespace Acts::IntegrationTest
diff --git a/Tests/IntegrationTests/PropagationDatasets.hpp b/Tests/IntegrationTests/PropagationDatasets.hpp
index 5c3bacb94cf..6b65e21c85f 100644
--- a/Tests/IntegrationTests/PropagationDatasets.hpp
+++ b/Tests/IntegrationTests/PropagationDatasets.hpp
@@ -12,8 +12,7 @@
 
 #include "Acts/Definitions/Units.hpp"
 
-namespace ActsTests {
-namespace PropagationDatasets {
+namespace ActsTests::PropagationDatasets {
 
 namespace bdata = boost::unit_test::data;
 using namespace Acts::UnitLiterals;
@@ -47,5 +46,4 @@ const auto pathLength = bdata::make({1_cm, 10_cm});
 // magnetic field strength
 const auto magneticField = bdata::make({0.5_T, 2_T, 4_T});
 
-}  // namespace PropagationDatasets
-}  // namespace ActsTests
+}  // namespace ActsTests::PropagationDatasets
diff --git a/Tests/UnitTests/Benchmarks/BenchmarkTools.cpp b/Tests/UnitTests/Benchmarks/BenchmarkTools.cpp
index 85050d32b2d..2ae6911e390 100644
--- a/Tests/UnitTests/Benchmarks/BenchmarkTools.cpp
+++ b/Tests/UnitTests/Benchmarks/BenchmarkTools.cpp
@@ -19,8 +19,7 @@
 #include <sstream>
 #include <tuple>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Basic non-timing tests do not validate the core performance aspects of the
 // benchmark tools, but have the advantage of being runnable on any system.
@@ -296,5 +295,4 @@ BOOST_AUTO_TEST_CASE(assume_written) {
 
 BOOST_AUTO_TEST_SUITE_END()
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Clusterization/ClusterizationTests1D.cpp b/Tests/UnitTests/Core/Clusterization/ClusterizationTests1D.cpp
index 4dd55736ae4..760ee400041 100644
--- a/Tests/UnitTests/Core/Clusterization/ClusterizationTests1D.cpp
+++ b/Tests/UnitTests/Core/Clusterization/ClusterizationTests1D.cpp
@@ -21,8 +21,7 @@
 
 #include <boost/functional/hash.hpp>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 struct Cell1D {
   Cell1D(int colv) : col(colv) {}
@@ -129,5 +128,4 @@ BOOST_AUTO_TEST_CASE(Grid_1D_rand) {
   }
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Clusterization/ClusterizationTests2D.cpp b/Tests/UnitTests/Core/Clusterization/ClusterizationTests2D.cpp
index 97aa95c07a0..27cfb0fafa1 100644
--- a/Tests/UnitTests/Core/Clusterization/ClusterizationTests2D.cpp
+++ b/Tests/UnitTests/Core/Clusterization/ClusterizationTests2D.cpp
@@ -24,8 +24,7 @@
 
 #include <boost/functional/hash.hpp>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using Rectangle = std::array<int, 4>;
 
@@ -248,5 +247,4 @@ BOOST_AUTO_TEST_CASE(Grid_2D_rand) {
   }
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Detector/BlueprintHelperTests.cpp b/Tests/UnitTests/Core/Detector/BlueprintHelperTests.cpp
index 2c5da5edf00..0f704545e7b 100644
--- a/Tests/UnitTests/Core/Detector/BlueprintHelperTests.cpp
+++ b/Tests/UnitTests/Core/Detector/BlueprintHelperTests.cpp
@@ -15,11 +15,9 @@
 #include <exception>
 #include <fstream>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 class IInternalStructureBuilder {};
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
 
 BOOST_AUTO_TEST_SUITE(Experimental)
 
diff --git a/Tests/UnitTests/Core/Detector/BlueprintTests.cpp b/Tests/UnitTests/Core/Detector/BlueprintTests.cpp
index dfd7dbaebb6..a8d2acfcaaa 100644
--- a/Tests/UnitTests/Core/Detector/BlueprintTests.cpp
+++ b/Tests/UnitTests/Core/Detector/BlueprintTests.cpp
@@ -13,11 +13,9 @@
 
 #include <fstream>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 class IInternalStructureBuilder {};
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
 
 BOOST_AUTO_TEST_SUITE(Experimental)
 
diff --git a/Tests/UnitTests/Core/Detector/CylindricalDetectorHelperTests.cpp b/Tests/UnitTests/Core/Detector/CylindricalDetectorHelperTests.cpp
index 66583ba2432..6b3e7173134 100644
--- a/Tests/UnitTests/Core/Detector/CylindricalDetectorHelperTests.cpp
+++ b/Tests/UnitTests/Core/Detector/CylindricalDetectorHelperTests.cpp
@@ -36,11 +36,9 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 class Portal;
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
 
 using namespace Acts;
 using namespace Experimental;
diff --git a/Tests/UnitTests/Core/Detector/PortalTests.cpp b/Tests/UnitTests/Core/Detector/PortalTests.cpp
index b9837b8e65b..fb710f1307d 100644
--- a/Tests/UnitTests/Core/Detector/PortalTests.cpp
+++ b/Tests/UnitTests/Core/Detector/PortalTests.cpp
@@ -31,8 +31,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 
 /// a simple link to volume struct
 class LinkToVolumeImpl : public INavigationDelegate {
@@ -50,8 +49,7 @@ class LinkToVolumeImpl : public INavigationDelegate {
   }
 };
 
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
 
 using namespace Acts::Experimental;
 
diff --git a/Tests/UnitTests/Core/Digitization/CartesianSegmentationTests.cpp b/Tests/UnitTests/Core/Digitization/CartesianSegmentationTests.cpp
index 4caa3b7072a..ae7fa0abee1 100644
--- a/Tests/UnitTests/Core/Digitization/CartesianSegmentationTests.cpp
+++ b/Tests/UnitTests/Core/Digitization/CartesianSegmentationTests.cpp
@@ -25,8 +25,7 @@
 
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 std::size_t nbinsx = 100;
 std::size_t nbinsy = 200;
@@ -127,5 +126,4 @@ BOOST_AUTO_TEST_CASE(cartesian_segmentation) {
   CHECK_CLOSE_REL(tAngle, lAngle, 0.001);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Digitization/PlanarModuleStepperTests.cpp b/Tests/UnitTests/Core/Digitization/PlanarModuleStepperTests.cpp
index e2ab9e5f073..7151c8842b4 100644
--- a/Tests/UnitTests/Core/Digitization/PlanarModuleStepperTests.cpp
+++ b/Tests/UnitTests/Core/Digitization/PlanarModuleStepperTests.cpp
@@ -29,8 +29,7 @@
 namespace bdata = boost::unit_test::data;
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 double halfX = 5_mm;
 double halfY = 10_mm;
@@ -104,5 +103,4 @@ BOOST_DATA_TEST_CASE(
   }
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/AlignmentContextTests.cpp b/Tests/UnitTests/Core/Geometry/AlignmentContextTests.cpp
index a176b5a82cc..929f746377b 100644
--- a/Tests/UnitTests/Core/Geometry/AlignmentContextTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/AlignmentContextTests.cpp
@@ -26,8 +26,7 @@ class PlanarBounds;
 
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 /// @class AlignmentContext
 struct AlignmentContext {
@@ -210,5 +209,4 @@ BOOST_AUTO_TEST_CASE(AlignmentContextTests) {
   BOOST_CHECK_EQUAL(localPosition, Vector2(3., 3.));
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/CuboidVolumeBoundsTests.cpp b/Tests/UnitTests/Core/Geometry/CuboidVolumeBoundsTests.cpp
index 79b92e46ea8..df24dc264f1 100644
--- a/Tests/UnitTests/Core/Geometry/CuboidVolumeBoundsTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/CuboidVolumeBoundsTests.cpp
@@ -26,8 +26,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 GeometryContext gctx = GeometryContext();
 
@@ -204,5 +203,4 @@ BOOST_AUTO_TEST_CASE(CuboidVolumeBoundsSetValues) {
 
 BOOST_AUTO_TEST_SUITE_END()
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/CuboidVolumeBuilderTests.cpp b/Tests/UnitTests/Core/Geometry/CuboidVolumeBuilderTests.cpp
index 4e7b63ef296..746e140483b 100644
--- a/Tests/UnitTests/Core/Geometry/CuboidVolumeBuilderTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/CuboidVolumeBuilderTests.cpp
@@ -35,8 +35,7 @@
 
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 BOOST_AUTO_TEST_CASE(CuboidVolumeBuilderTest) {
   // Construct builder
@@ -236,5 +235,4 @@ BOOST_AUTO_TEST_CASE(CuboidVolumeBuilderTest) {
       volumeConfig2.name);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/CylinderVolumeBuilderTests.cpp b/Tests/UnitTests/Core/Geometry/CylinderVolumeBuilderTests.cpp
index b7888b59b7d..0dd4df5cf52 100644
--- a/Tests/UnitTests/Core/Geometry/CylinderVolumeBuilderTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/CylinderVolumeBuilderTests.cpp
@@ -15,8 +15,7 @@
 
 namespace bdata = boost::unit_test::data;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 /// Unit test for testing the wraps() function of the CylinderVolumeBuilder
 BOOST_DATA_TEST_CASE(
@@ -367,5 +366,4 @@ BOOST_DATA_TEST_CASE(
   BOOST_CHECK(Config0.overlapsInZ(Config7));
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/GenericApproachDescriptorTests.cpp b/Tests/UnitTests/Core/Geometry/GenericApproachDescriptorTests.cpp
index daa7a2944c3..3bdabe7e7cc 100644
--- a/Tests/UnitTests/Core/Geometry/GenericApproachDescriptorTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/GenericApproachDescriptorTests.cpp
@@ -30,10 +30,7 @@
 #include "../Surfaces/SurfaceStub.hpp"
 #include "LayerStub.hpp"
 
-namespace Acts {
-
-namespace Test {
-namespace Layers {
+namespace Acts::Test::Layers {
 
 // Build a default context for testing
 GeometryContext tgContext = GeometryContext();
@@ -118,7 +115,4 @@ BOOST_AUTO_TEST_CASE(GenericApproachNoOverstepping) {
 }
 
 BOOST_AUTO_TEST_SUITE_END()
-}  // namespace Layers
-}  // namespace Test
-
-}  // namespace Acts
+}  // namespace Acts::Test::Layers
diff --git a/Tests/UnitTests/Core/Geometry/GenericCuboidVolumeBoundsTests.cpp b/Tests/UnitTests/Core/Geometry/GenericCuboidVolumeBoundsTests.cpp
index c0cd0bb6c26..2fc5a25ca85 100644
--- a/Tests/UnitTests/Core/Geometry/GenericCuboidVolumeBoundsTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/GenericCuboidVolumeBoundsTests.cpp
@@ -29,8 +29,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 GeometryContext gctx = GeometryContext();
 
@@ -240,5 +239,4 @@ BOOST_AUTO_TEST_CASE(GenericCuboidVolumeBoundarySurfaces) {
 }
 
 BOOST_AUTO_TEST_SUITE_END()
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/GeometryIdentifierTests.cpp b/Tests/UnitTests/Core/Geometry/GeometryIdentifierTests.cpp
index 62e6010f5f5..fe6e4224ffe 100644
--- a/Tests/UnitTests/Core/Geometry/GeometryIdentifierTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/GeometryIdentifierTests.cpp
@@ -10,8 +10,7 @@
 
 #include "Acts/Geometry/GeometryIdentifier.hpp"
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 BOOST_AUTO_TEST_CASE(GeometryIdentifier_construct_default) {
   GeometryIdentifier id;
@@ -92,5 +91,4 @@ BOOST_AUTO_TEST_CASE(GeometryIdentifier_order) {
                  GeometryIdentifier(vol1).setSensitive(2u).setExtra(1u));
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/LayerCreatorTests.cpp b/Tests/UnitTests/Core/Geometry/LayerCreatorTests.cpp
index f150d5734bd..372132937a8 100644
--- a/Tests/UnitTests/Core/Geometry/LayerCreatorTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/LayerCreatorTests.cpp
@@ -44,8 +44,7 @@
 
 #include <boost/format.hpp>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -459,5 +458,4 @@ BOOST_FIXTURE_TEST_CASE(LayerCreator_barrelStagger, LayerCreatorFixture) {
 }
 
 BOOST_AUTO_TEST_SUITE_END()
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/LayerTests.cpp b/Tests/UnitTests/Core/Geometry/LayerTests.cpp
index 80894ecc1cd..4b931aab45c 100644
--- a/Tests/UnitTests/Core/Geometry/LayerTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/LayerTests.cpp
@@ -27,8 +27,7 @@
 #include "../Surfaces/SurfaceStub.hpp"
 #include "LayerStub.hpp"
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -102,5 +101,4 @@ BOOST_AUTO_TEST_CASE(LayerProperties) {
 
 BOOST_AUTO_TEST_SUITE_END()
 }  // namespace Layers
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/NavigationLayerTests.cpp b/Tests/UnitTests/Core/Geometry/NavigationLayerTests.cpp
index 86f831d6b32..b40677975ea 100644
--- a/Tests/UnitTests/Core/Geometry/NavigationLayerTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/NavigationLayerTests.cpp
@@ -22,8 +22,7 @@
 
 #include "../Surfaces/SurfaceStub.hpp"
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -73,5 +72,4 @@ BOOST_AUTO_TEST_CASE(NavigationLayerProperties) {
 
 BOOST_AUTO_TEST_SUITE_END()
 }  // namespace Layers
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/PlaneLayerTests.cpp b/Tests/UnitTests/Core/Geometry/PlaneLayerTests.cpp
index 73cef2a790d..dba38bc4e52 100644
--- a/Tests/UnitTests/Core/Geometry/PlaneLayerTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/PlaneLayerTests.cpp
@@ -28,8 +28,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -97,5 +96,4 @@ BOOST_AUTO_TEST_CASE(PlaneLayerProperties) {
 
 BOOST_AUTO_TEST_SUITE_END()
 }  // namespace Layers
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/SimpleGeometryTests.cpp b/Tests/UnitTests/Core/Geometry/SimpleGeometryTests.cpp
index 63fabde2023..a8fe3cb2955 100644
--- a/Tests/UnitTests/Core/Geometry/SimpleGeometryTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/SimpleGeometryTests.cpp
@@ -29,8 +29,7 @@
 
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -121,5 +120,4 @@ BOOST_AUTO_TEST_CASE(SimpleGeometryTest) {
 
   BOOST_CHECK(tGeometry != nullptr);
 }
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/SurfaceArrayCreatorTests.cpp b/Tests/UnitTests/Core/Geometry/SurfaceArrayCreatorTests.cpp
index cfcf22b6e85..8ef383b3d62 100644
--- a/Tests/UnitTests/Core/Geometry/SurfaceArrayCreatorTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/SurfaceArrayCreatorTests.cpp
@@ -50,8 +50,7 @@
 using Acts::VectorHelpers::perp;
 using Acts::VectorHelpers::phi;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -731,5 +730,4 @@ BOOST_FIXTURE_TEST_CASE(SurfaceArrayCreator_barrelStagger,
 }
 
 BOOST_AUTO_TEST_SUITE_END()
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/SurfaceBinningMatcherTests.cpp b/Tests/UnitTests/Core/Geometry/SurfaceBinningMatcherTests.cpp
index 366d2ddaf1c..6133931eab0 100644
--- a/Tests/UnitTests/Core/Geometry/SurfaceBinningMatcherTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/SurfaceBinningMatcherTests.cpp
@@ -23,9 +23,7 @@
 
 #include <boost/format.hpp>
 
-namespace Acts {
-
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -78,6 +76,4 @@ BOOST_AUTO_TEST_CASE(PlaneSurfaceMatcher) {
       sbm(tgContext, binPhi, oneSurface.get(), similarPhiSurface.get()));
 }
 
-}  // namespace Test
-
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/TrackingGeometryClosureTests.cpp b/Tests/UnitTests/Core/Geometry/TrackingGeometryClosureTests.cpp
index 0e969a48bfc..99c38ff0663 100644
--- a/Tests/UnitTests/Core/Geometry/TrackingGeometryClosureTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/TrackingGeometryClosureTests.cpp
@@ -29,8 +29,7 @@
 
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -321,5 +320,4 @@ BOOST_AUTO_TEST_CASE(TrackingGeometry_testVisitSurfaces) {
   BOOST_CHECK_EQUAL(nVolumes, 5u);
 }
 
-}  //  end of namespace Test
-}  //  end of namespace Acts
+}  //  namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/TrackingGeometryCreationTests.cpp b/Tests/UnitTests/Core/Geometry/TrackingGeometryCreationTests.cpp
index 9fd97515d0c..46af559ff1a 100644
--- a/Tests/UnitTests/Core/Geometry/TrackingGeometryCreationTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/TrackingGeometryCreationTests.cpp
@@ -12,8 +12,7 @@
 #include "Acts/Tests/CommonHelpers/CubicTrackingGeometry.hpp"
 #include "Acts/Tests/CommonHelpers/CylindricalTrackingGeometry.hpp"
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -30,5 +29,4 @@ BOOST_AUTO_TEST_CASE(CubicTrackingGeometryTest) {
   BOOST_CHECK_NE(tGeometry, nullptr);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/TrackingGeometryGeometryIdTests.cpp b/Tests/UnitTests/Core/Geometry/TrackingGeometryGeometryIdTests.cpp
index d376a2544c3..ab015dd01a8 100644
--- a/Tests/UnitTests/Core/Geometry/TrackingGeometryGeometryIdTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/TrackingGeometryGeometryIdTests.cpp
@@ -26,8 +26,7 @@
 
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -138,5 +137,4 @@ BOOST_AUTO_TEST_CASE(GeometryIdentifier_containervolume_test) {
   }
 }
 
-}  //  end of namespace Test
-}  //  end of namespace Acts
+}  //  namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Geometry/VolumeTests.cpp b/Tests/UnitTests/Core/Geometry/VolumeTests.cpp
index ed719db4eac..0d98444fe7f 100644
--- a/Tests/UnitTests/Core/Geometry/VolumeTests.cpp
+++ b/Tests/UnitTests/Core/Geometry/VolumeTests.cpp
@@ -21,8 +21,7 @@
 #include <memory>
 #include <utility>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 BOOST_AUTO_TEST_CASE(VolumeTest) {
   using namespace Acts::UnitLiterals;
@@ -76,5 +75,4 @@ BOOST_AUTO_TEST_CASE(VolumeTest) {
   BOOST_CHECK_EQUAL(volume.binningPosition(gctx, binX), volume.center());
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/MagneticField/ConstantBFieldTests.cpp b/Tests/UnitTests/Core/MagneticField/ConstantBFieldTests.cpp
index 7018cce7d09..01f034369c0 100644
--- a/Tests/UnitTests/Core/MagneticField/ConstantBFieldTests.cpp
+++ b/Tests/UnitTests/Core/MagneticField/ConstantBFieldTests.cpp
@@ -22,8 +22,7 @@
 namespace bdata = boost::unit_test::data;
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 MagneticFieldContext mfContext = MagneticFieldContext();
@@ -122,5 +121,4 @@ BOOST_DATA_TEST_CASE(
   BOOST_CHECK_EQUAL(Btrue, BField.getField(-2 * pos, bCache).value());
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/MagneticField/InterpolatedBFieldMapTests.cpp b/Tests/UnitTests/Core/MagneticField/InterpolatedBFieldMapTests.cpp
index 80351759345..4a6ad3df443 100644
--- a/Tests/UnitTests/Core/MagneticField/InterpolatedBFieldMapTests.cpp
+++ b/Tests/UnitTests/Core/MagneticField/InterpolatedBFieldMapTests.cpp
@@ -32,8 +32,7 @@
 
 using Acts::VectorHelpers::perp;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 MagneticFieldContext mfContext = MagneticFieldContext();
@@ -170,5 +169,4 @@ BOOST_AUTO_TEST_CASE(InterpolatedBFieldMap_rz) {
   BOOST_CHECK(c.isInside(transformPos((pos << 0, 2, -4.7).finished())));
   BOOST_CHECK(!c.isInside(transformPos((pos << 5, 2, 14.).finished())));
 }
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/MagneticField/MagneticFieldProviderTests.cpp b/Tests/UnitTests/Core/MagneticField/MagneticFieldProviderTests.cpp
index e601660c7bb..a57275d08b7 100644
--- a/Tests/UnitTests/Core/MagneticField/MagneticFieldProviderTests.cpp
+++ b/Tests/UnitTests/Core/MagneticField/MagneticFieldProviderTests.cpp
@@ -11,8 +11,7 @@
 #include "Acts/MagneticField/MagneticFieldContext.hpp"
 #include "Acts/MagneticField/MagneticFieldProvider.hpp"
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 MagneticFieldContext mfContext = MagneticFieldContext();
@@ -52,5 +51,4 @@ BOOST_AUTO_TEST_CASE(TypeErasedCacheType) {
   BOOST_CHECK(destructor_called);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/MagneticField/SolenoidBFieldTests.cpp b/Tests/UnitTests/Core/MagneticField/SolenoidBFieldTests.cpp
index aa5d9f3b92d..d66b8097060 100644
--- a/Tests/UnitTests/Core/MagneticField/SolenoidBFieldTests.cpp
+++ b/Tests/UnitTests/Core/MagneticField/SolenoidBFieldTests.cpp
@@ -23,8 +23,7 @@
 
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 BOOST_AUTO_TEST_CASE(TestSolenoidBField) {
   // Create a test context
@@ -111,5 +110,4 @@ BOOST_AUTO_TEST_CASE(TestSolenoidBField) {
   // outf.close();
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Material/AccumulatedSurfaceMaterialTests.cpp b/Tests/UnitTests/Core/Material/AccumulatedSurfaceMaterialTests.cpp
index 82db7010121..b5f41f55185 100644
--- a/Tests/UnitTests/Core/Material/AccumulatedSurfaceMaterialTests.cpp
+++ b/Tests/UnitTests/Core/Material/AccumulatedSurfaceMaterialTests.cpp
@@ -21,8 +21,7 @@
 #include <memory>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 /// Test the constructors
 BOOST_AUTO_TEST_CASE(AccumulatedSurfaceMaterial_construction_test) {
@@ -186,5 +185,4 @@ BOOST_AUTO_TEST_CASE(AccumulatedSurfaceMaterial_variance_0D) {
   BOOST_CHECK_EQUAL(trackCount, 2u);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Material/BinnedSurfaceMaterialTests.cpp b/Tests/UnitTests/Core/Material/BinnedSurfaceMaterialTests.cpp
index c332318bda7..1468cb8f0b9 100644
--- a/Tests/UnitTests/Core/Material/BinnedSurfaceMaterialTests.cpp
+++ b/Tests/UnitTests/Core/Material/BinnedSurfaceMaterialTests.cpp
@@ -17,9 +17,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-
-namespace Test {
+namespace Acts::Test {
 
 /// Test the constructors
 BOOST_AUTO_TEST_CASE(BinnedSurfaceMaterial_construction_test) {
@@ -59,5 +57,4 @@ BOOST_AUTO_TEST_CASE(BinnedSurfaceMaterial_construction_test) {
   BinnedSurfaceMaterial bsmMoveAssigned(std::move(bsmAssigned));
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Material/HomogeneousSurfaceMaterialTests.cpp b/Tests/UnitTests/Core/Material/HomogeneousSurfaceMaterialTests.cpp
index 88dbbad476f..aa31a88f46c 100644
--- a/Tests/UnitTests/Core/Material/HomogeneousSurfaceMaterialTests.cpp
+++ b/Tests/UnitTests/Core/Material/HomogeneousSurfaceMaterialTests.cpp
@@ -18,9 +18,7 @@
 
 #include <utility>
 
-namespace Acts {
-
-namespace Test {
+namespace Acts::Test {
 
 /// Test the constructors
 BOOST_AUTO_TEST_CASE(HomogeneousSurfaceMaterial_construction_test) {
@@ -172,5 +170,4 @@ BOOST_AUTO_TEST_CASE(HomogeneousSurfaceMaterial_access_test) {
   BOOST_CHECK_EQUAL(mat, matFwdPre);
   BOOST_CHECK_EQUAL(vacuum, matBwdPre);
 }
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Material/HomogeneousVolumeMaterialTests.cpp b/Tests/UnitTests/Core/Material/HomogeneousVolumeMaterialTests.cpp
index 0a8cb8eecbb..09fac3c8e54 100644
--- a/Tests/UnitTests/Core/Material/HomogeneousVolumeMaterialTests.cpp
+++ b/Tests/UnitTests/Core/Material/HomogeneousVolumeMaterialTests.cpp
@@ -14,9 +14,7 @@
 
 #include <utility>
 
-namespace Acts {
-
-namespace Test {
+namespace Acts::Test {
 
 /// Test the constructors
 BOOST_AUTO_TEST_CASE(HomogeneousVolumeMaterial_construction_test) {
@@ -56,5 +54,4 @@ BOOST_AUTO_TEST_CASE(HomogeneousVolumeMaterial_access_test) {
   // Test equality of the copy
   BOOST_CHECK_EQUAL(mat, mat3d);
 }
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Material/ISurfaceMaterialTests.cpp b/Tests/UnitTests/Core/Material/ISurfaceMaterialTests.cpp
index 824eab95c26..24bb823db74 100644
--- a/Tests/UnitTests/Core/Material/ISurfaceMaterialTests.cpp
+++ b/Tests/UnitTests/Core/Material/ISurfaceMaterialTests.cpp
@@ -17,9 +17,7 @@
 #include <cstddef>
 #include <ostream>
 
-namespace Acts {
-
-namespace Test {
+namespace Acts::Test {
 
 class SurfaceMaterialStub : public ISurfaceMaterial {
   using ISurfaceMaterial::ISurfaceMaterial;
@@ -70,5 +68,4 @@ BOOST_AUTO_TEST_CASE(ISurfaceMaterial_factor_test) {
       1 - splitFactor);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Material/InterpolatedMaterialMapTests.cpp b/Tests/UnitTests/Core/Material/InterpolatedMaterialMapTests.cpp
index 4739d4c17e7..912d76f9957 100644
--- a/Tests/UnitTests/Core/Material/InterpolatedMaterialMapTests.cpp
+++ b/Tests/UnitTests/Core/Material/InterpolatedMaterialMapTests.cpp
@@ -28,9 +28,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-
-namespace Test {
+namespace Acts::Test {
 
 constexpr unsigned int dim = 2;
 using grid_t = Grid<Acts::Material::ParametersVector, detail::EquidistantAxis,
@@ -168,6 +166,4 @@ BOOST_AUTO_TEST_CASE(InterpolatedMaterialMap_test) {
   BOOST_CHECK_EQUAL(ipolMatMap.isInside(Vector3(0., 4., 0.)), false);
   BOOST_CHECK_EQUAL(ipolMatMap.isInside(Vector3(0., 0., 4.)), true);
 }
-}  // namespace Test
-
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Material/IntersectionMaterialAssignerTests.cpp b/Tests/UnitTests/Core/Material/IntersectionMaterialAssignerTests.cpp
index 99198dcc82d..0f692efe5ac 100644
--- a/Tests/UnitTests/Core/Material/IntersectionMaterialAssignerTests.cpp
+++ b/Tests/UnitTests/Core/Material/IntersectionMaterialAssignerTests.cpp
@@ -23,8 +23,7 @@
 
 #include <limits>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 auto tContext = GeometryContext();
 auto mContext = MagneticFieldContext();
@@ -94,5 +93,4 @@ BOOST_AUTO_TEST_CASE(FindDetectorVolumeIntersections) {
 
 BOOST_AUTO_TEST_SUITE_END()
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Material/MaterialGridHelperTests.cpp b/Tests/UnitTests/Core/Material/MaterialGridHelperTests.cpp
index 8f9aee24e9d..4f76a425714 100644
--- a/Tests/UnitTests/Core/Material/MaterialGridHelperTests.cpp
+++ b/Tests/UnitTests/Core/Material/MaterialGridHelperTests.cpp
@@ -26,8 +26,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using EAxis = Acts::detail::EquidistantAxis;
 using Grid2D = Acts::Grid<Acts::AccumulatedVolumeMaterial, EAxis, EAxis>;
@@ -412,5 +411,4 @@ BOOST_AUTO_TEST_CASE(Cylindrical_Grid_test) {
   BOOST_CHECK_EQUAL(matMap.atLocalBins(index3), vacuum.parameters());
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Material/MaterialInteractionAssignmentTests.cpp b/Tests/UnitTests/Core/Material/MaterialInteractionAssignmentTests.cpp
index 603884bd41b..9187453734c 100644
--- a/Tests/UnitTests/Core/Material/MaterialInteractionAssignmentTests.cpp
+++ b/Tests/UnitTests/Core/Material/MaterialInteractionAssignmentTests.cpp
@@ -22,8 +22,7 @@
 
 #include <limits>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 auto tContext = GeometryContext();
 
@@ -302,5 +301,4 @@ BOOST_AUTO_TEST_CASE(AssignWithPathLength) {
 
 BOOST_AUTO_TEST_SUITE_END()
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Material/PropagatorMaterialAssignerTests.cpp b/Tests/UnitTests/Core/Material/PropagatorMaterialAssignerTests.cpp
index a10959a6af5..7c1c031fb4b 100644
--- a/Tests/UnitTests/Core/Material/PropagatorMaterialAssignerTests.cpp
+++ b/Tests/UnitTests/Core/Material/PropagatorMaterialAssignerTests.cpp
@@ -35,8 +35,7 @@
 
 #include <limits>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 auto tContext = GeometryContext();
 auto mContext = MagneticFieldContext();
@@ -203,5 +202,4 @@ BOOST_AUTO_TEST_CASE(FindSurfaceIntersectionsTrackingVolume) {
 
 BOOST_AUTO_TEST_SUITE_END()
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Material/ProtoSurfaceMaterialTests.cpp b/Tests/UnitTests/Core/Material/ProtoSurfaceMaterialTests.cpp
index e50d38429ab..bb084a3ccd1 100644
--- a/Tests/UnitTests/Core/Material/ProtoSurfaceMaterialTests.cpp
+++ b/Tests/UnitTests/Core/Material/ProtoSurfaceMaterialTests.cpp
@@ -14,9 +14,7 @@
 
 #include <utility>
 
-namespace Acts {
-
-namespace Test {
+namespace Acts::Test {
 
 /// Test the constructors
 BOOST_AUTO_TEST_CASE(ProtoSurfaceMaterial_construction_test) {
@@ -31,5 +29,4 @@ BOOST_AUTO_TEST_CASE(ProtoSurfaceMaterial_construction_test) {
   ProtoSurfaceMaterial smpCopyMoved(std::move(smpCopy));
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Material/ProtoVolumeMaterialTests.cpp b/Tests/UnitTests/Core/Material/ProtoVolumeMaterialTests.cpp
index 5b4b1c76622..d075e4db2d5 100644
--- a/Tests/UnitTests/Core/Material/ProtoVolumeMaterialTests.cpp
+++ b/Tests/UnitTests/Core/Material/ProtoVolumeMaterialTests.cpp
@@ -14,9 +14,7 @@
 
 #include <utility>
 
-namespace Acts {
-
-namespace Test {
+namespace Acts::Test {
 
 /// Test the constructors
 BOOST_AUTO_TEST_CASE(ProtoVolumeMaterial_construction_test) {
@@ -32,5 +30,4 @@ BOOST_AUTO_TEST_CASE(ProtoVolumeMaterial_construction_test) {
   ProtoVolumeMaterial vmpCopyMoved(std::move(vmpCopy));
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Navigation/DetectorVolumeUpdatersTests.cpp b/Tests/UnitTests/Core/Navigation/DetectorVolumeUpdatersTests.cpp
index c6e8963333b..abe8ca8a0f3 100644
--- a/Tests/UnitTests/Core/Navigation/DetectorVolumeUpdatersTests.cpp
+++ b/Tests/UnitTests/Core/Navigation/DetectorVolumeUpdatersTests.cpp
@@ -22,11 +22,9 @@
 // A test context
 Acts::GeometryContext tContext;
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 class DetectorVolume {};
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
 
 auto volumeA = std::make_shared<Acts::Experimental::DetectorVolume>();
 auto volumeB = std::make_shared<Acts::Experimental::DetectorVolume>();
diff --git a/Tests/UnitTests/Core/Navigation/NavigationStateTests.cpp b/Tests/UnitTests/Core/Navigation/NavigationStateTests.cpp
index 0fce099f478..e9f1f1b35aa 100644
--- a/Tests/UnitTests/Core/Navigation/NavigationStateTests.cpp
+++ b/Tests/UnitTests/Core/Navigation/NavigationStateTests.cpp
@@ -19,12 +19,10 @@
 #include <memory>
 #include <vector>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 /// Define a dummy detector volume
 class DetectorVolume {};
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
 
 BOOST_AUTO_TEST_SUITE(Experimental)
 
diff --git a/Tests/UnitTests/Core/Propagator/AtlasStepperTests.cpp b/Tests/UnitTests/Core/Propagator/AtlasStepperTests.cpp
index 0d58576b9a5..a2895ebb50a 100644
--- a/Tests/UnitTests/Core/Propagator/AtlasStepperTests.cpp
+++ b/Tests/UnitTests/Core/Propagator/AtlasStepperTests.cpp
@@ -48,8 +48,7 @@
 #include <type_traits>
 #include <utility>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using namespace Acts::UnitLiterals;
 using Acts::VectorHelpers::makeVector4;
@@ -609,5 +608,4 @@ BOOST_AUTO_TEST_CASE(StepSizeSurface) {
 
 BOOST_AUTO_TEST_SUITE_END()
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Propagator/AuctioneerTests.cpp b/Tests/UnitTests/Core/Propagator/AuctioneerTests.cpp
index c8d41abc78d..8d3a96158ea 100644
--- a/Tests/UnitTests/Core/Propagator/AuctioneerTests.cpp
+++ b/Tests/UnitTests/Core/Propagator/AuctioneerTests.cpp
@@ -12,8 +12,7 @@
 
 #include <array>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 BOOST_AUTO_TEST_CASE(AuctioneerTest_VoidAuctioneer) {
   // Build arbitrary vector
@@ -50,5 +49,4 @@ BOOST_AUTO_TEST_CASE(AuctioneerTest_HighestValidAuctioneer) {
   BOOST_CHECK_EQUAL_COLLECTIONS(expected.begin(), expected.end(),
                                 resultFva.begin(), resultFva.end());
 }
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Propagator/ConstrainedStepTests.cpp b/Tests/UnitTests/Core/Propagator/ConstrainedStepTests.cpp
index c1567ec3a5c..6a703bf28f3 100644
--- a/Tests/UnitTests/Core/Propagator/ConstrainedStepTests.cpp
+++ b/Tests/UnitTests/Core/Propagator/ConstrainedStepTests.cpp
@@ -14,8 +14,7 @@
 
 #include <limits>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // This tests the implementation of the AbortList
 // and the standard aborters
@@ -60,5 +59,4 @@ BOOST_AUTO_TEST_CASE(ConstrainedStepTest) {
   BOOST_CHECK_EQUAL(stepSize_p.value(), 0.05);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Propagator/CovarianceEngineTests.cpp b/Tests/UnitTests/Core/Propagator/CovarianceEngineTests.cpp
index ebc6bea28ea..7dbe9b979d9 100644
--- a/Tests/UnitTests/Core/Propagator/CovarianceEngineTests.cpp
+++ b/Tests/UnitTests/Core/Propagator/CovarianceEngineTests.cpp
@@ -37,8 +37,7 @@
 
 namespace bdata = boost::unit_test::data;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 Acts::GeometryContext gctx;
 Acts::MagneticFieldContext mctx;
@@ -505,5 +504,4 @@ BOOST_DATA_TEST_CASE(CovarianceConversionPerigee,
   CHECK_CLOSE_ABS(covB, covC, 1e-7);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Propagator/DirectNavigatorTests.cpp b/Tests/UnitTests/Core/Propagator/DirectNavigatorTests.cpp
index 903553ba324..0ee45e58a2b 100644
--- a/Tests/UnitTests/Core/Propagator/DirectNavigatorTests.cpp
+++ b/Tests/UnitTests/Core/Propagator/DirectNavigatorTests.cpp
@@ -46,8 +46,7 @@ class Surface;
 namespace bdata = boost::unit_test::data;
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -200,5 +199,4 @@ BOOST_DATA_TEST_CASE(
   runTest(rpropagator, dpropagator, pT, phi, theta, charge, index);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Propagator/EigenStepperTests.cpp b/Tests/UnitTests/Core/Propagator/EigenStepperTests.cpp
index 656be3a684a..34b4b4a3348 100644
--- a/Tests/UnitTests/Core/Propagator/EigenStepperTests.cpp
+++ b/Tests/UnitTests/Core/Propagator/EigenStepperTests.cpp
@@ -75,8 +75,7 @@ class Logger;
 using namespace Acts::UnitLiterals;
 using Acts::VectorHelpers::makeVector4;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using Covariance = BoundSquareMatrix;
 
@@ -1155,5 +1154,4 @@ BOOST_AUTO_TEST_CASE(step_extension_trackercalomdt_test) {
     }
   }
 }
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Propagator/ExtrapolatorTests.cpp b/Tests/UnitTests/Core/Propagator/ExtrapolatorTests.cpp
index 7a77f0f83b6..14abef62502 100644
--- a/Tests/UnitTests/Core/Propagator/ExtrapolatorTests.cpp
+++ b/Tests/UnitTests/Core/Propagator/ExtrapolatorTests.cpp
@@ -46,8 +46,7 @@
 namespace bdata = boost::unit_test::data;
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -288,5 +287,4 @@ BOOST_DATA_TEST_CASE(
   }
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Propagator/JacobianEngineTests.cpp b/Tests/UnitTests/Core/Propagator/JacobianEngineTests.cpp
index cd5715287e3..8065d16a9bb 100644
--- a/Tests/UnitTests/Core/Propagator/JacobianEngineTests.cpp
+++ b/Tests/UnitTests/Core/Propagator/JacobianEngineTests.cpp
@@ -20,8 +20,7 @@
 #include <cmath>
 #include <memory>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 /// Helper function tests
 BOOST_AUTO_TEST_CASE(jacobian_engine_helper) {
@@ -265,5 +264,4 @@ BOOST_AUTO_TEST_CASE(jacobian_engine_to_free) {
   BOOST_CHECK(newFreeCovariance1.isApprox(newFreeCovariance2));
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Propagator/JacobianTests.cpp b/Tests/UnitTests/Core/Propagator/JacobianTests.cpp
index 701267c716d..e5791a7bff8 100644
--- a/Tests/UnitTests/Core/Propagator/JacobianTests.cpp
+++ b/Tests/UnitTests/Core/Propagator/JacobianTests.cpp
@@ -38,8 +38,7 @@
 
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using BFieldType = ConstantBField;
 using EigenStepperType = EigenStepper<>;
@@ -266,5 +265,4 @@ BOOST_AUTO_TEST_CASE(JacobianStrawToGlobalTest) {
   testJacobianToGlobal(atStraw);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Propagator/KalmanExtrapolatorTests.cpp b/Tests/UnitTests/Core/Propagator/KalmanExtrapolatorTests.cpp
index 2c99e603375..700caf744ee 100644
--- a/Tests/UnitTests/Core/Propagator/KalmanExtrapolatorTests.cpp
+++ b/Tests/UnitTests/Core/Propagator/KalmanExtrapolatorTests.cpp
@@ -42,8 +42,7 @@ struct EndOfWorldReached;
 
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using Jacobian = BoundMatrix;
 using Covariance = BoundSquareMatrix;
@@ -184,5 +183,4 @@ BOOST_AUTO_TEST_CASE(kalman_extrapolator) {
   CHECK_CLOSE_OR_SMALL(pJacobian, accJacobian, 1e-6, 1e-9);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Propagator/MaterialCollectionTests.cpp b/Tests/UnitTests/Core/Propagator/MaterialCollectionTests.cpp
index 5fea940e01f..f14679f77db 100644
--- a/Tests/UnitTests/Core/Propagator/MaterialCollectionTests.cpp
+++ b/Tests/UnitTests/Core/Propagator/MaterialCollectionTests.cpp
@@ -46,8 +46,7 @@
 namespace bdata = boost::unit_test::data;
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -407,5 +406,4 @@ BOOST_DATA_TEST_CASE(
   runTest(slpropagator, pT, phi, theta, charge, index);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Propagator/NavigatorTests.cpp b/Tests/UnitTests/Core/Propagator/NavigatorTests.cpp
index 4fe5a409c38..3f0aec61513 100644
--- a/Tests/UnitTests/Core/Propagator/NavigatorTests.cpp
+++ b/Tests/UnitTests/Core/Propagator/NavigatorTests.cpp
@@ -52,8 +52,7 @@ struct FreeToBoundCorrection;
 using namespace Acts::UnitLiterals;
 using Acts::VectorHelpers::perp;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -693,5 +692,4 @@ BOOST_AUTO_TEST_CASE(Navigator_target_methods) {
   }
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Propagator/PropagatorTests.cpp b/Tests/UnitTests/Core/Propagator/PropagatorTests.cpp
index d3de87fc51f..b314c313158 100644
--- a/Tests/UnitTests/Core/Propagator/PropagatorTests.cpp
+++ b/Tests/UnitTests/Core/Propagator/PropagatorTests.cpp
@@ -59,8 +59,7 @@ using namespace Acts::UnitLiterals;
 using Acts::VectorHelpers::makeVector4;
 using Acts::VectorHelpers::perp;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -485,5 +484,4 @@ BOOST_AUTO_TEST_CASE(BasicPropagatorInterface) {
                   "Propagator unexpectedly inherits from BasePropagator");
   }
 }
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Propagator/StraightLineStepperTests.cpp b/Tests/UnitTests/Core/Propagator/StraightLineStepperTests.cpp
index 54fb8ff3fe4..814806086ab 100644
--- a/Tests/UnitTests/Core/Propagator/StraightLineStepperTests.cpp
+++ b/Tests/UnitTests/Core/Propagator/StraightLineStepperTests.cpp
@@ -38,8 +38,7 @@
 
 using Acts::VectorHelpers::makeVector4;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using Covariance = BoundSquareMatrix;
 
@@ -392,5 +391,4 @@ BOOST_AUTO_TEST_CASE(straight_line_stepper_test) {
   CHECK_CLOSE_COVARIANCE(slsState.cov, Covariance(2. * cov), 1e-6);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Propagator/VolumeMaterialInteractionTests.cpp b/Tests/UnitTests/Core/Propagator/VolumeMaterialInteractionTests.cpp
index cbef61a954b..d37ac188324 100644
--- a/Tests/UnitTests/Core/Propagator/VolumeMaterialInteractionTests.cpp
+++ b/Tests/UnitTests/Core/Propagator/VolumeMaterialInteractionTests.cpp
@@ -25,8 +25,7 @@
 
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 /// @brief Simplified stepper state
 struct StepperState {
@@ -136,5 +135,4 @@ BOOST_AUTO_TEST_CASE(volume_material_interaction_test) {
   BOOST_CHECK_EQUAL(volMatInt.pathCorrection, 0.);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/SpacePointFormation/SpacePointBuilderTests.cpp b/Tests/UnitTests/Core/SpacePointFormation/SpacePointBuilderTests.cpp
index 95e3b4b4b51..1d896999fbf 100644
--- a/Tests/UnitTests/Core/SpacePointFormation/SpacePointBuilderTests.cpp
+++ b/Tests/UnitTests/Core/SpacePointFormation/SpacePointBuilderTests.cpp
@@ -47,8 +47,7 @@
 
 namespace bdata = boost::unit_test::data;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using namespace UnitLiterals;
 
@@ -321,5 +320,4 @@ BOOST_DATA_TEST_CASE(SpacePointBuilder_basic, bdata::xrange(1), index) {
   BOOST_CHECK_EQUAL(spacePoints.size(), 6);
 }
 
-}  // end of namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Surfaces/AlignmentHelperTests.cpp b/Tests/UnitTests/Core/Surfaces/AlignmentHelperTests.cpp
index 451e0c89386..ada970908f3 100644
--- a/Tests/UnitTests/Core/Surfaces/AlignmentHelperTests.cpp
+++ b/Tests/UnitTests/Core/Surfaces/AlignmentHelperTests.cpp
@@ -16,8 +16,7 @@
 #include <cmath>
 #include <utility>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 /// Test for rotation matrix and calculation of derivative of rotated x/y/z axis
 /// w.r.t. rotation parameters
@@ -123,5 +122,4 @@ BOOST_AUTO_TEST_CASE(alignment_helper_test) {
   // Check if the derivative for local z axis is as expected
   CHECK_CLOSE_ABS(irotToLocalZAxis, expRotToZAxis, 1e-15);
 }
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Surfaces/ConeSurfaceTests.cpp b/Tests/UnitTests/Core/Surfaces/ConeSurfaceTests.cpp
index 9b104c603df..691d60a6619 100644
--- a/Tests/UnitTests/Core/Surfaces/ConeSurfaceTests.cpp
+++ b/Tests/UnitTests/Core/Surfaces/ConeSurfaceTests.cpp
@@ -30,8 +30,7 @@
 
 // using boost::test_tools::output_test_stream;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -276,5 +275,4 @@ BOOST_AUTO_TEST_CASE(ConeSurfaceAlignment) {
 }
 
 BOOST_AUTO_TEST_SUITE_END()
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Surfaces/CylinderSurfaceTests.cpp b/Tests/UnitTests/Core/Surfaces/CylinderSurfaceTests.cpp
index 35199eda4bb..afd5257d46c 100644
--- a/Tests/UnitTests/Core/Surfaces/CylinderSurfaceTests.cpp
+++ b/Tests/UnitTests/Core/Surfaces/CylinderSurfaceTests.cpp
@@ -38,8 +38,7 @@ namespace Acts {
 class AssertionFailureException;
 }  // namespace Acts
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext testContext = GeometryContext();
@@ -329,6 +328,4 @@ BOOST_AUTO_TEST_CASE(CylinderSurfaceBinningPosition) {
 
 BOOST_AUTO_TEST_SUITE_END()
 
-}  // namespace Test
-
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Surfaces/PerigeeSurfaceTests.cpp b/Tests/UnitTests/Core/Surfaces/PerigeeSurfaceTests.cpp
index 43219963b34..4e5024c2f24 100644
--- a/Tests/UnitTests/Core/Surfaces/PerigeeSurfaceTests.cpp
+++ b/Tests/UnitTests/Core/Surfaces/PerigeeSurfaceTests.cpp
@@ -18,8 +18,7 @@
 #include <memory>
 #include <string>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -90,5 +89,4 @@ BOOST_AUTO_TEST_CASE(EqualityOperators) {
 }
 
 BOOST_AUTO_TEST_SUITE_END()
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Surfaces/PlaneSurfaceTests.cpp b/Tests/UnitTests/Core/Surfaces/PlaneSurfaceTests.cpp
index e365d4325b4..f4e3727fcb1 100644
--- a/Tests/UnitTests/Core/Surfaces/PlaneSurfaceTests.cpp
+++ b/Tests/UnitTests/Core/Surfaces/PlaneSurfaceTests.cpp
@@ -37,8 +37,7 @@
 
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -361,6 +360,4 @@ BOOST_AUTO_TEST_CASE(PlaneSurfaceAlignment) {
 
 BOOST_AUTO_TEST_SUITE_END()
 
-}  // namespace Test
-
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Surfaces/StrawSurfaceTests.cpp b/Tests/UnitTests/Core/Surfaces/StrawSurfaceTests.cpp
index 383e52a0e39..b58985e2e9a 100644
--- a/Tests/UnitTests/Core/Surfaces/StrawSurfaceTests.cpp
+++ b/Tests/UnitTests/Core/Surfaces/StrawSurfaceTests.cpp
@@ -27,9 +27,7 @@ class PlanarBounds;
 
 namespace utf = boost::unit_test;
 
-namespace Acts {
-
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -132,6 +130,4 @@ BOOST_AUTO_TEST_CASE(EqualityOperators) {
 
 BOOST_AUTO_TEST_SUITE_END()
 
-}  // namespace Test
-
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Surfaces/SurfaceArrayTests.cpp b/Tests/UnitTests/Core/Surfaces/SurfaceArrayTests.cpp
index a56b9ccdfe3..b41a17b786b 100644
--- a/Tests/UnitTests/Core/Surfaces/SurfaceArrayTests.cpp
+++ b/Tests/UnitTests/Core/Surfaces/SurfaceArrayTests.cpp
@@ -40,9 +40,7 @@
 
 using Acts::VectorHelpers::phi;
 
-namespace Acts {
-
-namespace Test {
+namespace Acts::Test {
 
 // Create a test context
 GeometryContext tgContext = GeometryContext();
@@ -277,6 +275,4 @@ BOOST_AUTO_TEST_CASE(SurfaceArray_manyElementsSingleLookup) {
 }
 
 BOOST_AUTO_TEST_SUITE_END()
-}  // namespace Test
-
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/TrackFitting/Gx2fTests.cpp b/Tests/UnitTests/Core/TrackFitting/Gx2fTests.cpp
index d9af10cdd97..52b836d0fc7 100644
--- a/Tests/UnitTests/Core/TrackFitting/Gx2fTests.cpp
+++ b/Tests/UnitTests/Core/TrackFitting/Gx2fTests.cpp
@@ -42,8 +42,7 @@ using namespace Acts::detail::Test;
 Acts::Logging::Level logLevel = Acts::Logging::VERBOSE;
 const auto gx2fLogger = Acts::getDefaultLogger("Gx2f", logLevel);
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 //// Construct initial track parameters.
 Acts::CurvilinearTrackParameters makeParameters(
@@ -804,5 +803,4 @@ BOOST_AUTO_TEST_CASE(NotEnoughMeasurements) {
   ACTS_INFO("*** Test: NotEnoughMeasurements -- Finish");
 }
 BOOST_AUTO_TEST_SUITE_END()
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Utilities/AnnealingUtilityTests.cpp b/Tests/UnitTests/Core/Utilities/AnnealingUtilityTests.cpp
index e84ad10f777..cad4c95765e 100644
--- a/Tests/UnitTests/Core/Utilities/AnnealingUtilityTests.cpp
+++ b/Tests/UnitTests/Core/Utilities/AnnealingUtilityTests.cpp
@@ -15,8 +15,7 @@
 #include <iostream>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 BOOST_AUTO_TEST_CASE(annealing_tool_singleChi2_tests) {
   std::vector<double> temperatures{64., 16., 4., 2., 1.5, 1.};
@@ -176,5 +175,4 @@ BOOST_AUTO_TEST_CASE(annealing_tool_multiChi2_tests) {
   }
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Utilities/BinAdjustmentTests.cpp b/Tests/UnitTests/Core/Utilities/BinAdjustmentTests.cpp
index 699868204b2..34c3bea2803 100644
--- a/Tests/UnitTests/Core/Utilities/BinAdjustmentTests.cpp
+++ b/Tests/UnitTests/Core/Utilities/BinAdjustmentTests.cpp
@@ -21,8 +21,7 @@
 #include <memory>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Test Radial
 BOOST_AUTO_TEST_CASE(BinAdjustment_Radial) {
@@ -84,5 +83,4 @@ BOOST_AUTO_TEST_CASE(BinAdjustment_Trapezoid) {
   BOOST_CHECK_EQUAL(buAdjust.binningData()[1].max, 30);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Utilities/BinAdjustmentVolumeTests.cpp b/Tests/UnitTests/Core/Utilities/BinAdjustmentVolumeTests.cpp
index 49531e2248a..07c8310aecd 100644
--- a/Tests/UnitTests/Core/Utilities/BinAdjustmentVolumeTests.cpp
+++ b/Tests/UnitTests/Core/Utilities/BinAdjustmentVolumeTests.cpp
@@ -20,8 +20,7 @@
 #include <memory>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // Test Cylinder
 BOOST_AUTO_TEST_CASE(BinAdjustmentVolume_Cylinder) {
@@ -77,5 +76,4 @@ BOOST_AUTO_TEST_CASE(BinAdjustmentVolume_Cuboid) {
   BOOST_CHECK_EQUAL(buAdjust.binningData()[2].max, 42);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Utilities/BinUtilityTests.cpp b/Tests/UnitTests/Core/Utilities/BinUtilityTests.cpp
index 525777ee345..882fc5703c6 100644
--- a/Tests/UnitTests/Core/Utilities/BinUtilityTests.cpp
+++ b/Tests/UnitTests/Core/Utilities/BinUtilityTests.cpp
@@ -18,8 +18,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // OPEN - equidistant binning tests
 BOOST_AUTO_TEST_CASE(BinUtility_equidistant_binning) {
@@ -128,5 +127,4 @@ BOOST_AUTO_TEST_CASE(BinUtility_transform) {
   }
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Utilities/BinningDataTests.cpp b/Tests/UnitTests/Core/Utilities/BinningDataTests.cpp
index 1645819ad62..ebea495abf8 100644
--- a/Tests/UnitTests/Core/Utilities/BinningDataTests.cpp
+++ b/Tests/UnitTests/Core/Utilities/BinningDataTests.cpp
@@ -19,8 +19,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // the test positions in 3D
 Vector3 xyzPosition(0.5, 1.5, 2.5);
@@ -403,5 +402,4 @@ BOOST_AUTO_TEST_CASE(BinningData_phi_modules) {
   BOOST_CHECK_EQUAL(phiData_mod.searchGlobal(underscaledPos), std::size_t(4));
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Utilities/BoundingBoxTest.cpp b/Tests/UnitTests/Core/Utilities/BoundingBoxTest.cpp
index b7bbedfece9..5f2e4e46b6b 100644
--- a/Tests/UnitTests/Core/Utilities/BoundingBoxTest.cpp
+++ b/Tests/UnitTests/Core/Utilities/BoundingBoxTest.cpp
@@ -32,8 +32,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 struct Object {};
 
@@ -1256,5 +1255,4 @@ BOOST_AUTO_TEST_CASE(ostream_operator) {
   BOOST_CHECK(ss.str() == "AABB(ctr=(0.5, 0.5) vmin=(-1, -1) vmax=(2, 2))");
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Utilities/DBScanTests.cpp b/Tests/UnitTests/Core/Utilities/DBScanTests.cpp
index ab47c630d62..efd502a464a 100644
--- a/Tests/UnitTests/Core/Utilities/DBScanTests.cpp
+++ b/Tests/UnitTests/Core/Utilities/DBScanTests.cpp
@@ -74,8 +74,7 @@ std::vector<std::array<double, 2>> test_vector{
     {6.55276593, -7.81387909},  {-1.79854507, -2.10170986}};
 }  // namespace
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 BOOST_AUTO_TEST_CASE(ClusteringTest2D) {
   using DBSCAN = Acts::DBScan<2, double, 4>;
@@ -104,5 +103,4 @@ BOOST_AUTO_TEST_CASE(ClusteringTest2D) {
   clusteredPoints.clear();
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Utilities/ExtendableTests.cpp b/Tests/UnitTests/Core/Utilities/ExtendableTests.cpp
index bb42909d1e6..445ef1cb4ad 100644
--- a/Tests/UnitTests/Core/Utilities/ExtendableTests.cpp
+++ b/Tests/UnitTests/Core/Utilities/ExtendableTests.cpp
@@ -15,8 +15,7 @@
 #include <tuple>
 #include <type_traits>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 // This tests the implementation of the ActionList
 // and the standard aborters
@@ -59,5 +58,4 @@ BOOST_AUTO_TEST_CASE(Extendable_) {
   BOOST_CHECK_EQUAL(abcList.get<TypeC>().vaC, '4');
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Utilities/FiniteStateMachineTests.cpp b/Tests/UnitTests/Core/Utilities/FiniteStateMachineTests.cpp
index 5c54160c3c9..e633c2db5a1 100644
--- a/Tests/UnitTests/Core/Utilities/FiniteStateMachineTests.cpp
+++ b/Tests/UnitTests/Core/Utilities/FiniteStateMachineTests.cpp
@@ -14,8 +14,7 @@
 #include <optional>
 #include <stdexcept>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 namespace states {
 struct Disconnected {};
@@ -298,5 +297,4 @@ BOOST_AUTO_TEST_CASE(InternalTransitions) {
 
 BOOST_AUTO_TEST_SUITE_END()
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Utilities/HashedStringTests.cpp b/Tests/UnitTests/Core/Utilities/HashedStringTests.cpp
index 7428e585055..d2570aa4068 100644
--- a/Tests/UnitTests/Core/Utilities/HashedStringTests.cpp
+++ b/Tests/UnitTests/Core/Utilities/HashedStringTests.cpp
@@ -15,9 +15,7 @@
 
 using namespace Acts::HashedStringLiteral;
 
-namespace Acts {
-
-namespace Test {
+namespace Acts::Test {
 
 BOOST_AUTO_TEST_CASE(string_hashes) {
   // compile time checks
@@ -36,6 +34,4 @@ BOOST_AUTO_TEST_CASE(string_hashes) {
   static_assert(hashString(sv) == 440920331, "Invalid");
 }
 
-}  // namespace Test
-
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Utilities/IntersectionTests.cpp b/Tests/UnitTests/Core/Utilities/IntersectionTests.cpp
index 7d149307d26..c2f9afe75e2 100644
--- a/Tests/UnitTests/Core/Utilities/IntersectionTests.cpp
+++ b/Tests/UnitTests/Core/Utilities/IntersectionTests.cpp
@@ -23,8 +23,7 @@
 #include <string>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 class Object {};
 
@@ -202,5 +201,4 @@ BOOST_AUTO_TEST_CASE(IntersectionStatusPrinting) {
   }
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Utilities/KDTreeTests.cpp b/Tests/UnitTests/Core/Utilities/KDTreeTests.cpp
index 20979d4dab7..9c4a4d2fe64 100644
--- a/Tests/UnitTests/Core/Utilities/KDTreeTests.cpp
+++ b/Tests/UnitTests/Core/Utilities/KDTreeTests.cpp
@@ -73,8 +73,7 @@ std::vector<std::pair<std::array<double, 3>, int>> test_vector{
     {{-6.0, 3.5, -7.4}, 7},    {{3.2, -6.2, 3.9}, -25}};
 }
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 struct TreeFixture1DDoubleInt1 {
   TreeFixture1DDoubleInt1()
@@ -634,5 +633,4 @@ BOOST_AUTO_TEST_CASE(range_search_many_same) {
 BOOST_AUTO_TEST_SUITE_END()
 
 BOOST_AUTO_TEST_SUITE_END()
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Utilities/LoggerTests.cpp b/Tests/UnitTests/Core/Utilities/LoggerTests.cpp
index 7d82a3681dc..e6451b547cf 100644
--- a/Tests/UnitTests/Core/Utilities/LoggerTests.cpp
+++ b/Tests/UnitTests/Core/Utilities/LoggerTests.cpp
@@ -20,8 +20,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using namespace Acts::Logging;
 
@@ -146,5 +145,4 @@ BOOST_AUTO_TEST_CASE(DEBUG_test) {
 BOOST_AUTO_TEST_CASE(VERBOSE_test) {
   debug_level_test("verbose_log.txt", VERBOSE);
 }
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Utilities/MaterialMapUtilsTests.cpp b/Tests/UnitTests/Core/Utilities/MaterialMapUtilsTests.cpp
index 26278984275..4f9c3561ca2 100644
--- a/Tests/UnitTests/Core/Utilities/MaterialMapUtilsTests.cpp
+++ b/Tests/UnitTests/Core/Utilities/MaterialMapUtilsTests.cpp
@@ -21,8 +21,7 @@
 
 namespace bdata = boost::unit_test::data;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 BOOST_AUTO_TEST_CASE(materialmap_creation) {
   // Create grid values
@@ -125,5 +124,4 @@ BOOST_AUTO_TEST_CASE(materialmap_creation) {
   CHECK_CLOSE_ABS(value1_xyz.parameters(), mat1_xyz.parameters(), 1e-9);
   CHECK_CLOSE_ABS(value2_xyz.parameters(), mat2_xyz.parameters(), 1e-9);
 }
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Vertexing/AdaptiveGridTrackDensityTests.cpp b/Tests/UnitTests/Core/Vertexing/AdaptiveGridTrackDensityTests.cpp
index 2277197ce1a..cccf8c08c18 100644
--- a/Tests/UnitTests/Core/Vertexing/AdaptiveGridTrackDensityTests.cpp
+++ b/Tests/UnitTests/Core/Vertexing/AdaptiveGridTrackDensityTests.cpp
@@ -27,8 +27,7 @@
 namespace bdata = boost::unit_test::data;
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using Covariance = BoundSquareMatrix;
 
@@ -649,5 +648,4 @@ BOOST_AUTO_TEST_CASE(track_removing) {
   CHECK_CLOSE_ABS(0., sixthDensitySum2D, 1e-4);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Vertexing/AdaptiveMultiVertexFinderTests.cpp b/Tests/UnitTests/Core/Vertexing/AdaptiveMultiVertexFinderTests.cpp
index 71afa1f4813..a2b9dcef060 100644
--- a/Tests/UnitTests/Core/Vertexing/AdaptiveMultiVertexFinderTests.cpp
+++ b/Tests/UnitTests/Core/Vertexing/AdaptiveMultiVertexFinderTests.cpp
@@ -55,8 +55,7 @@
 
 #include "VertexingDataHelper.hpp"
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using namespace Acts::UnitLiterals;
 
@@ -671,5 +670,4 @@ BOOST_AUTO_TEST_CASE(
   }
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Vertexing/AdaptiveMultiVertexFitterTests.cpp b/Tests/UnitTests/Core/Vertexing/AdaptiveMultiVertexFitterTests.cpp
index c52ec3cded2..7c67926603e 100644
--- a/Tests/UnitTests/Core/Vertexing/AdaptiveMultiVertexFitterTests.cpp
+++ b/Tests/UnitTests/Core/Vertexing/AdaptiveMultiVertexFitterTests.cpp
@@ -49,8 +49,7 @@
 #include <utility>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using namespace Acts::UnitLiterals;
 using Acts::VectorHelpers::makeVector4;
@@ -733,5 +732,4 @@ BOOST_AUTO_TEST_CASE(adaptive_multi_vertex_fitter_test_athena) {
   CHECK_CLOSE_ABS(vtx2FQ.second, expVtx2ndf, 0.001);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Vertexing/FullBilloirVertexFitterTests.cpp b/Tests/UnitTests/Core/Vertexing/FullBilloirVertexFitterTests.cpp
index ae15fc109d2..981aed262db 100644
--- a/Tests/UnitTests/Core/Vertexing/FullBilloirVertexFitterTests.cpp
+++ b/Tests/UnitTests/Core/Vertexing/FullBilloirVertexFitterTests.cpp
@@ -48,8 +48,7 @@
 namespace bdata = boost::unit_test::data;
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using Covariance = BoundSquareMatrix;
 
@@ -297,5 +296,4 @@ BOOST_AUTO_TEST_CASE(billoir_vertex_fitter_defaulttrack_test) {
     }
   }
 }
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Vertexing/GaussianGridTrackDensityTests.cpp b/Tests/UnitTests/Core/Vertexing/GaussianGridTrackDensityTests.cpp
index e9f059d5263..8bdba7c18e8 100644
--- a/Tests/UnitTests/Core/Vertexing/GaussianGridTrackDensityTests.cpp
+++ b/Tests/UnitTests/Core/Vertexing/GaussianGridTrackDensityTests.cpp
@@ -30,8 +30,7 @@
 namespace bdata = boost::unit_test::data;
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using Covariance = BoundSquareMatrix;
 
@@ -309,5 +308,4 @@ BOOST_AUTO_TEST_CASE(gaussian_grid_seed_width_test) {
   BOOST_CHECK_NE(width, 0.);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Vertexing/GridDensityVertexFinderTests.cpp b/Tests/UnitTests/Core/Vertexing/GridDensityVertexFinderTests.cpp
index 6e260e5fc06..d40b7cb036d 100644
--- a/Tests/UnitTests/Core/Vertexing/GridDensityVertexFinderTests.cpp
+++ b/Tests/UnitTests/Core/Vertexing/GridDensityVertexFinderTests.cpp
@@ -42,8 +42,7 @@ namespace bdata = boost::unit_test::data;
 using namespace Acts::UnitLiterals;
 using Acts::VectorHelpers::makeVector4;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using Covariance = BoundSquareMatrix;
 
@@ -482,5 +481,4 @@ BOOST_AUTO_TEST_CASE(grid_density_vertex_finder_seed_width_test) {
   CHECK_CLOSE_ABS(covZZ1, covZZ2, 1e-4);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Vertexing/IterativeVertexFinderTests.cpp b/Tests/UnitTests/Core/Vertexing/IterativeVertexFinderTests.cpp
index f14fe5b180b..fd11b9e470c 100644
--- a/Tests/UnitTests/Core/Vertexing/IterativeVertexFinderTests.cpp
+++ b/Tests/UnitTests/Core/Vertexing/IterativeVertexFinderTests.cpp
@@ -59,8 +59,7 @@
 namespace bdata = boost::unit_test::data;
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using Covariance = BoundSquareMatrix;
 using Propagator = Acts::Propagator<EigenStepper<>>;
@@ -646,5 +645,4 @@ BOOST_AUTO_TEST_CASE(iterative_finder_test_athena_reference) {
   // }
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Vertexing/KalmanVertexUpdaterTests.cpp b/Tests/UnitTests/Core/Vertexing/KalmanVertexUpdaterTests.cpp
index 88e956ceb72..ca88b35a147 100644
--- a/Tests/UnitTests/Core/Vertexing/KalmanVertexUpdaterTests.cpp
+++ b/Tests/UnitTests/Core/Vertexing/KalmanVertexUpdaterTests.cpp
@@ -47,8 +47,7 @@
 namespace bdata = boost::unit_test::data;
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using Covariance = BoundSquareMatrix;
 using Propagator = Acts::Propagator<EigenStepper<>>;
@@ -329,5 +328,4 @@ BOOST_AUTO_TEST_CASE(Kalman_Vertex_TrackUpdater) {
 
 }  // end test case
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Vertexing/LinearizedTrackFactoryTests.cpp b/Tests/UnitTests/Core/Vertexing/LinearizedTrackFactoryTests.cpp
index 7ee6e4a3b2b..46b762aeca0 100644
--- a/Tests/UnitTests/Core/Vertexing/LinearizedTrackFactoryTests.cpp
+++ b/Tests/UnitTests/Core/Vertexing/LinearizedTrackFactoryTests.cpp
@@ -44,8 +44,7 @@
 namespace bdata = boost::unit_test::data;
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using Covariance = BoundSquareMatrix;
 // We will compare analytical and numerical computations in the case of a
@@ -277,5 +276,4 @@ BOOST_AUTO_TEST_CASE(linearized_track_factory_test) {
   }
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Vertexing/TrackDensityVertexFinderTests.cpp b/Tests/UnitTests/Core/Vertexing/TrackDensityVertexFinderTests.cpp
index 44249fb1cc6..94c37e32b1d 100644
--- a/Tests/UnitTests/Core/Vertexing/TrackDensityVertexFinderTests.cpp
+++ b/Tests/UnitTests/Core/Vertexing/TrackDensityVertexFinderTests.cpp
@@ -45,8 +45,7 @@ namespace bdata = boost::unit_test::data;
 using namespace Acts::UnitLiterals;
 using Acts::VectorHelpers::makeVector4;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using Covariance = BoundSquareMatrix;
 
@@ -372,5 +371,4 @@ BOOST_AUTO_TEST_CASE(track_density_finder_usertrack_test) {
   }
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Vertexing/VertexingDataHelper.hpp b/Tests/UnitTests/Core/Vertexing/VertexingDataHelper.hpp
index 89f93b5ac18..de0963c14bd 100644
--- a/Tests/UnitTests/Core/Vertexing/VertexingDataHelper.hpp
+++ b/Tests/UnitTests/Core/Vertexing/VertexingDataHelper.hpp
@@ -17,8 +17,7 @@
 #include <iterator>
 #include <regex>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using namespace Acts::UnitLiterals;
 using Covariance = BoundSquareMatrix;
@@ -147,5 +146,4 @@ readTracksAndVertexCSV(const std::string& toolString,
   return std::make_tuple(beamspotConstraint, vertices, tracks);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Vertexing/ZScanVertexFinderTests.cpp b/Tests/UnitTests/Core/Vertexing/ZScanVertexFinderTests.cpp
index 3ae2042bfb2..b9bca4a9c37 100644
--- a/Tests/UnitTests/Core/Vertexing/ZScanVertexFinderTests.cpp
+++ b/Tests/UnitTests/Core/Vertexing/ZScanVertexFinderTests.cpp
@@ -49,8 +49,7 @@
 namespace bdata = boost::unit_test::data;
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 using Covariance = BoundSquareMatrix;
 using Propagator = Acts::Propagator<EigenStepper<>>;
@@ -314,5 +313,4 @@ BOOST_AUTO_TEST_CASE(zscan_finder_usertrack_test) {
   }
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Visualization/EventDataView3DBase.hpp b/Tests/UnitTests/Core/Visualization/EventDataView3DBase.hpp
index 5c103322625..2b08150ad6e 100644
--- a/Tests/UnitTests/Core/Visualization/EventDataView3DBase.hpp
+++ b/Tests/UnitTests/Core/Visualization/EventDataView3DBase.hpp
@@ -47,8 +47,7 @@
 
 using Acts::VectorHelpers::makeVector4;
 
-namespace Acts {
-namespace EventDataView3DTest {
+namespace Acts::EventDataView3DTest {
 
 using Covariance = BoundSquareMatrix;
 
@@ -400,5 +399,4 @@ static inline std::string testMultiTrajectory(IVisualization3D& helper) {
   return ss.str();
 }
 
-}  // namespace EventDataView3DTest
-}  // namespace Acts
+}  // namespace Acts::EventDataView3DTest
diff --git a/Tests/UnitTests/Core/Visualization/PrimitivesView3DBase.hpp b/Tests/UnitTests/Core/Visualization/PrimitivesView3DBase.hpp
index f3ae1cf1b98..505646cfd75 100644
--- a/Tests/UnitTests/Core/Visualization/PrimitivesView3DBase.hpp
+++ b/Tests/UnitTests/Core/Visualization/PrimitivesView3DBase.hpp
@@ -22,9 +22,7 @@
 #include <sstream>
 #include <string>
 
-namespace Acts {
-
-namespace PrimitivesView3DTest {
+namespace Acts::PrimitivesView3DTest {
 
 // Test on a plane
 auto identity = Transform3::Identity();
@@ -117,5 +115,4 @@ static inline std::string run(IVisualization3D& helper) {
   return ss.str();
 }
 
-}  // namespace PrimitivesView3DTest
-}  // namespace Acts
+}  // namespace Acts::PrimitivesView3DTest
diff --git a/Tests/UnitTests/Core/Visualization/SurfaceView3DBase.hpp b/Tests/UnitTests/Core/Visualization/SurfaceView3DBase.hpp
index f1e7902ec88..8de0a7fda5a 100644
--- a/Tests/UnitTests/Core/Visualization/SurfaceView3DBase.hpp
+++ b/Tests/UnitTests/Core/Visualization/SurfaceView3DBase.hpp
@@ -32,9 +32,7 @@
 #include <sstream>
 #include <string>
 
-namespace Acts {
-
-namespace SurfaceView3DTest {
+namespace Acts::SurfaceView3DTest {
 
 /// Helper method to visualize all types of surfaces
 ///
@@ -500,5 +498,4 @@ static inline std::string run(IVisualization3D& helper, bool triangulate,
   return cStream.str();
 }
 
-}  // namespace SurfaceView3DTest
-}  // namespace Acts
+}  // namespace Acts::SurfaceView3DTest
diff --git a/Tests/UnitTests/Core/Visualization/TrackingGeometryView3DBase.hpp b/Tests/UnitTests/Core/Visualization/TrackingGeometryView3DBase.hpp
index 884523acc97..350e08e1490 100644
--- a/Tests/UnitTests/Core/Visualization/TrackingGeometryView3DBase.hpp
+++ b/Tests/UnitTests/Core/Visualization/TrackingGeometryView3DBase.hpp
@@ -18,9 +18,7 @@
 #include <sstream>
 #include <string>
 
-namespace Acts {
-
-namespace TrackingGeometryView3DTest {
+namespace Acts::TrackingGeometryView3DTest {
 
 GeometryContext tgContext = GeometryContext();
 
@@ -66,5 +64,4 @@ static inline std::string run(IVisualization3D& helper, bool triangulate,
   return cStream.str();
 }
 
-}  // namespace TrackingGeometryView3DTest
-}  // namespace Acts
+}  // namespace Acts::TrackingGeometryView3DTest
diff --git a/Tests/UnitTests/Core/Visualization/Visualization3DTester.hpp b/Tests/UnitTests/Core/Visualization/Visualization3DTester.hpp
index 7cf27eed7af..84f4c2046c2 100644
--- a/Tests/UnitTests/Core/Visualization/Visualization3DTester.hpp
+++ b/Tests/UnitTests/Core/Visualization/Visualization3DTester.hpp
@@ -15,9 +15,7 @@
 
 #include <boost/algorithm/string.hpp>
 
-namespace Acts {
-
-namespace Test {
+namespace Acts::Test {
 
 /// This is a test function that tests the validity of an obj stream
 /// It tests for special characters that are not allowed to be contained
@@ -226,6 +224,4 @@ inline static std::vector<std::string> testPlyString(const std::string& tString,
   return errorStrings;
 }
 
-}  // namespace Test
-
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Core/Visualization/VolumeView3DBase.hpp b/Tests/UnitTests/Core/Visualization/VolumeView3DBase.hpp
index 6397c7a1d9f..00745012f74 100644
--- a/Tests/UnitTests/Core/Visualization/VolumeView3DBase.hpp
+++ b/Tests/UnitTests/Core/Visualization/VolumeView3DBase.hpp
@@ -21,9 +21,7 @@
 #include <sstream>
 #include <string>
 
-namespace Acts {
-
-namespace VolumeView3DTest {
+namespace Acts::VolumeView3DTest {
 
 /// Helper method to visualize all types of surfaces
 ///
@@ -181,5 +179,4 @@ static inline std::string run(IVisualization3D& helper, bool triangulate,
   return cStream.str();
 }
 
-}  // namespace VolumeView3DTest
-}  // namespace Acts
+}  // namespace Acts::VolumeView3DTest
diff --git a/Tests/UnitTests/Fatras/Kernel/TupleIndexOfTests.cpp b/Tests/UnitTests/Fatras/Kernel/TupleIndexOfTests.cpp
index 5f1748119f6..baf49ab6bdf 100644
--- a/Tests/UnitTests/Fatras/Kernel/TupleIndexOfTests.cpp
+++ b/Tests/UnitTests/Fatras/Kernel/TupleIndexOfTests.cpp
@@ -12,12 +12,10 @@
 
 #include <tuple>
 
-namespace ActsFatras {
-namespace detail {
+namespace ActsFatras::detail {
 template <class T, class Tuple>
 struct TupleIndexOf;
-}  // namespace detail
-}  // namespace ActsFatras
+}  // namespace ActsFatras::detail
 
 using ActsFatras::detail::TupleIndexOf;
 
diff --git a/Tests/UnitTests/Plugins/Json/PortalJsonConverterTests.cpp b/Tests/UnitTests/Plugins/Json/PortalJsonConverterTests.cpp
index ae59c4bcc97..374e81a9c5a 100644
--- a/Tests/UnitTests/Plugins/Json/PortalJsonConverterTests.cpp
+++ b/Tests/UnitTests/Plugins/Json/PortalJsonConverterTests.cpp
@@ -22,11 +22,9 @@
 
 #include <nlohmann/json.hpp>
 
-namespace Acts {
-namespace Experimental {
+namespace Acts::Experimental {
 class DetectorVolume {};
-}  // namespace Experimental
-}  // namespace Acts
+}  // namespace Acts::Experimental
 
 Acts::GeometryContext tContext;
 
diff --git a/Tests/UnitTests/Plugins/TGeo/TGeoArb8ConversionTests.cpp b/Tests/UnitTests/Plugins/TGeo/TGeoArb8ConversionTests.cpp
index 4d5093b721d..651b19ab316 100644
--- a/Tests/UnitTests/Plugins/TGeo/TGeoArb8ConversionTests.cpp
+++ b/Tests/UnitTests/Plugins/TGeo/TGeoArb8ConversionTests.cpp
@@ -33,9 +33,7 @@
 #include "TGeoVolume.h"
 #include "TView.h"
 
-namespace Acts {
-
-namespace Test {
+namespace Acts::Test {
 
 GeometryContext tgContext = GeometryContext();
 
@@ -115,6 +113,4 @@ BOOST_AUTO_TEST_CASE(TGeoArb8_to_PlaneSurface) {
   }
 }
 
-}  // namespace Test
-
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Plugins/TGeo/TGeoBBoxConversionTests.cpp b/Tests/UnitTests/Plugins/TGeo/TGeoBBoxConversionTests.cpp
index 0bcd6daa77d..fcd96763043 100644
--- a/Tests/UnitTests/Plugins/TGeo/TGeoBBoxConversionTests.cpp
+++ b/Tests/UnitTests/Plugins/TGeo/TGeoBBoxConversionTests.cpp
@@ -32,8 +32,7 @@
 #include "TGeoVolume.h"
 #include "TView.h"
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 GeometryContext tgContext = GeometryContext();
 
@@ -213,6 +212,4 @@ BOOST_AUTO_TEST_CASE(TGeoBBox_to_PlaneSurface) {
   objVis.write("TGeoConversion_TGeoBBox_PlaneSurface");
 }
 
-}  // namespace Test
-
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Plugins/TGeo/TGeoLayerBuilderTests.cpp b/Tests/UnitTests/Plugins/TGeo/TGeoLayerBuilderTests.cpp
index b948a639283..ccea59c4323 100644
--- a/Tests/UnitTests/Plugins/TGeo/TGeoLayerBuilderTests.cpp
+++ b/Tests/UnitTests/Plugins/TGeo/TGeoLayerBuilderTests.cpp
@@ -34,9 +34,7 @@
 
 using namespace Acts::UnitLiterals;
 
-namespace Acts {
-
-namespace Test {
+namespace Acts::Test {
 
 /// @brief struct to load the global geometry
 struct RootGeometry {
@@ -119,6 +117,4 @@ BOOST_AUTO_TEST_CASE(TGeoLayerBuilderTests) {
   }
 }
 
-}  // namespace Test
-
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Plugins/TGeo/TGeoParserTests.cpp b/Tests/UnitTests/Plugins/TGeo/TGeoParserTests.cpp
index 043de958851..99ae9c2c2d8 100644
--- a/Tests/UnitTests/Plugins/TGeo/TGeoParserTests.cpp
+++ b/Tests/UnitTests/Plugins/TGeo/TGeoParserTests.cpp
@@ -24,9 +24,7 @@
 
 #include "TGeoManager.h"
 
-namespace Acts {
-
-namespace Test {
+namespace Acts::Test {
 
 /// @brief struct to load the global geometry
 struct RootGeometry {
@@ -109,5 +107,4 @@ BOOST_AUTO_TEST_CASE(TGeoParser_Pixel_SelectInnermost) {
   }
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Plugins/TGeo/TGeoPrimitivesHelperTests.cpp b/Tests/UnitTests/Plugins/TGeo/TGeoPrimitivesHelperTests.cpp
index f25f6828d55..bf895d28eb4 100644
--- a/Tests/UnitTests/Plugins/TGeo/TGeoPrimitivesHelperTests.cpp
+++ b/Tests/UnitTests/Plugins/TGeo/TGeoPrimitivesHelperTests.cpp
@@ -14,8 +14,7 @@
 #include <string>
 #include <vector>
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 /// @brief Unit test checking the match probability
 BOOST_AUTO_TEST_CASE(TGeoPrimitivesHelper_match) {
@@ -27,5 +26,4 @@ BOOST_AUTO_TEST_CASE(TGeoPrimitivesHelper_match) {
   BOOST_CHECK(TGeoPrimitivesHelper::match(candidates, "BeamPipe"));
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Plugins/TGeo/TGeoTrd1ConversionTests.cpp b/Tests/UnitTests/Plugins/TGeo/TGeoTrd1ConversionTests.cpp
index 6e883f9334b..4b19a2c55bd 100644
--- a/Tests/UnitTests/Plugins/TGeo/TGeoTrd1ConversionTests.cpp
+++ b/Tests/UnitTests/Plugins/TGeo/TGeoTrd1ConversionTests.cpp
@@ -37,8 +37,7 @@
 #include "TGeoVolume.h"
 #include "TView.h"
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 GeometryContext tgContext = GeometryContext();
 
@@ -112,5 +111,4 @@ BOOST_AUTO_TEST_CASE(TGeoTrd1_to_PlaneSurface) {
   objVis.write("TGeoConversion_TGeoTrd1_PlaneSurface");
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Plugins/TGeo/TGeoTrd2ConversionTests.cpp b/Tests/UnitTests/Plugins/TGeo/TGeoTrd2ConversionTests.cpp
index dd3f65eff00..d32b7ec5fe0 100644
--- a/Tests/UnitTests/Plugins/TGeo/TGeoTrd2ConversionTests.cpp
+++ b/Tests/UnitTests/Plugins/TGeo/TGeoTrd2ConversionTests.cpp
@@ -37,8 +37,7 @@
 #include "TGeoVolume.h"
 #include "TView.h"
 
-namespace Acts {
-namespace Test {
+namespace Acts::Test {
 
 GeometryContext tgContext = GeometryContext();
 
@@ -180,5 +179,4 @@ BOOST_AUTO_TEST_CASE(TGeoTrd2_yz_to_PlaneSurface) {
   }
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/Tests/UnitTests/Plugins/TGeo/TGeoTubeConversionTests.cpp b/Tests/UnitTests/Plugins/TGeo/TGeoTubeConversionTests.cpp
index fb8a9aeb1e3..73305cc507d 100644
--- a/Tests/UnitTests/Plugins/TGeo/TGeoTubeConversionTests.cpp
+++ b/Tests/UnitTests/Plugins/TGeo/TGeoTubeConversionTests.cpp
@@ -37,9 +37,7 @@
 #include "TGeoVolume.h"
 #include "TView.h"
 
-namespace Acts {
-
-namespace Test {
+namespace Acts::Test {
 
 GeometryContext tgContext = GeometryContext();
 
@@ -250,6 +248,4 @@ BOOST_AUTO_TEST_CASE(TGeoTube_to_DiscSurface) {
   }
 }
 
-}  // namespace Test
-
-}  // namespace Acts
+}  // namespace Acts::Test
diff --git a/cmake/ActsStaticAnalysis.cmake b/cmake/ActsStaticAnalysis.cmake
index 075adf125e9..b5464a9a5e0 100644
--- a/cmake/ActsStaticAnalysis.cmake
+++ b/cmake/ActsStaticAnalysis.cmake
@@ -14,6 +14,7 @@ if(ACTS_RUN_CLANG_TIDY)
     list(APPEND _chks "readability-braces-around-statements")
     list(APPEND _chks "readability-implicit-bool-cast")
     list(APPEND _chks "readability-implicit-bool-conversion")
+    list(APPEND _chks "modernize-concat-nested-namespaces")
     list(APPEND _chks "modernize-use-using")
     list(APPEND _chks "modernize-use-override")
     list(APPEND _chks "modernize-use-equals-default")