diff --git a/src/Graph.php b/src/Graph.php
index 8ce325ea..784e21fc 100644
--- a/src/Graph.php
+++ b/src/Graph.php
@@ -27,6 +27,11 @@ class Graph implements DualAggregate, AttributeAware
 
     protected $attributes = array();
 
+    /**
+     * @var Group[]
+     */
+    protected $groups = array();
+
     public function __construct()
     {
         $this->vertices = VerticesMap::factoryArrayReference($this->verticesStorage);
@@ -466,4 +471,33 @@ public function getAttributeBag()
     {
         return new AttributeBagReference($this->attributes);
     }
+
+    /**
+     * @param int|string $groupId
+     * @param bool $returnDuplicate
+     * @return Group
+     */
+    public function createGroup($groupId, $returnDuplicate = false)
+    {
+        if ($returnDuplicate && isset($this->groups[$groupId])) {
+            return $this->groups[$groupId];
+        }
+
+        if (isset($this->groups[$groupId])) {
+            throw new OverflowException('Group already exists: ' . $groupId);
+        }
+
+        $group = new Group($this, $groupId);
+        $this->groups[$groupId] = $group;
+
+        return $group;
+    }
+
+    /**
+     * @return array|Group[]
+     */
+    public function getGroups()
+    {
+        return array_values($this->groups);
+    }
 }
diff --git a/src/Group.php b/src/Group.php
new file mode 100644
index 00000000..46a4c02c
--- /dev/null
+++ b/src/Group.php
@@ -0,0 +1,79 @@
+<?php
+
+namespace Fhaculty\Graph;
+
+use Fhaculty\Graph\Attribute\AttributeAware;
+use Fhaculty\Graph\Attribute\AttributeBagReference;
+use Fhaculty\Graph\Exception\InvalidArgumentException;
+
+class Group implements AttributeAware
+{
+    /**
+     * @var int|string
+     */
+    private $id;
+
+    /**
+     * @var Graph
+     */
+    private $graph;
+
+    private $attributes = array();
+
+    public function __construct(Graph $graph, $id)
+    {
+        if (!is_int($id) && !is_string($id)) {
+            throw new InvalidArgumentException('Group ID has to be of type integer or string');
+        }
+
+        $this->id = $id;
+        $this->graph = $graph;
+    }
+
+    public function getId()
+    {
+        return $this->id;
+    }
+
+    public function getVerticesInGroup()
+    {
+        $thisGroup = $this;
+
+        return array_values(array_filter(
+            $this->graph->getVertices()->getMap(),
+            function (Vertex $vertex) use ($thisGroup) {
+                return $vertex->getGroup() instanceof Group && $vertex->getGroup()->equals($thisGroup);
+            }
+        ));
+    }
+
+    public function getAttribute($name, $default = null)
+    {
+        return isset($this->attributes[$name]) ? $this->attributes[$name] : $default;
+    }
+
+    public function setAttribute($name, $value)
+    {
+        $this->attributes[$name] = $value;
+    }
+
+    public function removeAttribute($name)
+    {
+        unset($this->attributes[$name]);
+    }
+
+    public function getAttributeBag()
+    {
+        return new AttributeBagReference($this->attributes);
+    }
+
+    public function __toString()
+    {
+        return (string)$this->id;
+    }
+
+    public function equals(Group $other)
+    {
+        return $this->id === $other->id;
+    }
+}
diff --git a/src/Set/Vertices.php b/src/Set/Vertices.php
index e11a1f06..790287c5 100644
--- a/src/Set/Vertices.php
+++ b/src/Set/Vertices.php
@@ -2,6 +2,7 @@
 
 namespace Fhaculty\Graph\Set;
 
+use Fhaculty\Graph\Group;
 use Fhaculty\Graph\Vertex;
 use Fhaculty\Graph\Exception\InvalidArgumentException;
 use Fhaculty\Graph\Exception\OutOfBoundsException;
@@ -511,19 +512,16 @@ private function getCallback($callback)
             return $callback;
         }
 
-        static $methods = array(
-            self::ORDER_ID => 'getId',
-            self::ORDER_GROUP => 'getGroup'
-        );
-
-        if (!is_int($callback) || !isset($methods[$callback])) {
-            throw new InvalidArgumentException('Invalid callback given');
+        if ($callback === self::ORDER_ID) {
+            return function (Vertex $vertex) {
+                return $vertex->getId();
+            };
+        } elseif ($callback === self::ORDER_GROUP) {
+            return function (Vertex $vertex) {
+                return $vertex->getGroup() instanceof Group ? $vertex->getGroup()->getId() : null;
+            };
         }
 
-        $method = $methods[$callback];
-
-        return function (Vertex $vertex) use ($method) {
-            return $vertex->$method();
-        };
+        throw new InvalidArgumentException('Invalid callback given');
     }
 }
diff --git a/src/Vertex.php b/src/Vertex.php
index 13e5b9cf..4a27596e 100644
--- a/src/Vertex.php
+++ b/src/Vertex.php
@@ -36,12 +36,13 @@ class Vertex implements EdgesAggregate, AttributeAware
     private $balance;
 
     /**
-     * group number
+     * group
      *
-     * @var int
+     * @var Group|null
      * @see Vertex::setGroup()
+     * @see Vertex::getGroup()
      */
-    private $group = 0;
+    private $group;
 
     private $attributes = array();
 
@@ -90,26 +91,23 @@ public function setBalance($balance)
     }
 
     /**
-     * set group number of this vertex
+     * set group of this vertex
      *
-     * @param  int                      $group
+     * @param  Group|null               $group
      * @return Vertex                   $this (chainable)
      * @throws InvalidArgumentException if group is not numeric
      */
-    public function setGroup($group)
+    public function setGroup(Group $group = null)
     {
-        if (!is_int($group)) {
-            throw new InvalidArgumentException('Invalid group number');
-        }
         $this->group = $group;
 
         return $this;
     }
 
     /**
-     * get group number
+     * get group
      *
-     * @return int
+     * @return Group|null
      */
     public function getGroup()
     {
diff --git a/tests/GraphTest.php b/tests/GraphTest.php
index a8bea3bb..24f39af8 100644
--- a/tests/GraphTest.php
+++ b/tests/GraphTest.php
@@ -2,9 +2,11 @@
 
 namespace Fhaculty\Graph\Tests;
 
+use Fhaculty\Graph\Exception\OutOfBoundsException;
 use Fhaculty\Graph\Exception\OverflowException;
 use Fhaculty\Graph\Exception\InvalidArgumentException;
 use Fhaculty\Graph\Graph;
+use Fhaculty\Graph\Group;
 use Fhaculty\Graph\Tests\Attribute\AbstractAttributeAwareTest;
 
 class GraphTest extends AbstractAttributeAwareTest
@@ -17,7 +19,7 @@ public function setup()
     public function testVertexClone()
     {
         $graph = new Graph();
-        $vertex = $graph->createVertex(123)->setBalance(10)->setGroup(4);
+        $vertex = $graph->createVertex(123)->setBalance(10)->setGroup($graph->createGroup(4));
 
         $newgraph = new Graph();
         $newvertex = $newgraph->createVertexClone($vertex);
@@ -56,7 +58,7 @@ public function testGetVertexNonexistant()
     public function testGraphClone()
     {
         $graph = new Graph();
-        $graph->createVertex(123)->setBalance(10)->setGroup(4);
+        $graph->createVertex(123)->setBalance(10)->setGroup($graph->createGroup(4));
 
         $newgraph = $graph->createGraphClone();
 
@@ -391,6 +393,42 @@ public function testCreateGraphCloneVertices()
         $this->assertEquals(1, count($graphClone->getEdges()));
     }
 
+    public function testGetGroups()
+    {
+        $graph = new Graph();
+        $graph->createGroup(1);
+        $graph->createGroup(2);
+
+        $this->assertEquals(
+            array(
+                new Group($graph, 1),
+                new Group($graph, 2)
+            ),
+            $graph->getGroups()
+        );
+    }
+
+    public function testCreateGroupReturnDuplicate()
+    {
+        $graph = new Graph();
+        $alreadyCreated = $graph->createGroup(1);
+
+        $this->assertSame(
+            $alreadyCreated,
+            $graph->createGroup(1, true)
+        );
+    }
+
+    /**
+     * @expectedException OverflowException
+     */
+    public function testCreateGroupAlreadyExists()
+    {
+        $graph = new Graph();
+        $graph->createGroup(1);
+        $graph->createGroup(1);
+    }
+
     protected function createAttributeAware()
     {
         return new Graph();
diff --git a/tests/GroupTest.php b/tests/GroupTest.php
new file mode 100644
index 00000000..e3aff5b5
--- /dev/null
+++ b/tests/GroupTest.php
@@ -0,0 +1,77 @@
+<?php
+
+namespace Fhaculty\Graph\Tests;
+
+use Fhaculty\Graph\Exception\InvalidArgumentException;
+use Fhaculty\Graph\Graph;
+use Fhaculty\Graph\Group;
+use Fhaculty\Graph\Tests\Attribute\AbstractAttributeAwareTest;
+
+final class GroupTest extends AbstractAttributeAwareTest
+{
+    public function testGroupIdCanBeAnInteger()
+    {
+        $group = new Group(new Graph(), 1);
+
+        $this->assertSame(1, $group->getId());
+    }
+
+    public function testGroupIdCanBeAString()
+    {
+        $group = new Group(new Graph(), 'string');
+
+        $this->assertSame('string', $group->getId());
+    }
+
+    /**
+     * @expectedException InvalidArgumentException
+     */
+    public function testGroupIdCanNotBeSomethingElse()
+    {
+        new Group(new Graph(), null);
+    }
+
+    public function testGroupEquals()
+    {
+        $group = new Group(new Graph(), 1);
+
+        $this->assertTrue($group->equals(new Group(new Graph(), 1)));
+    }
+
+    public function testGroupIsNotEqual()
+    {
+        $group = new Group(new Graph(), 1);
+
+        $this->assertFalse($group->equals(new Group(new Graph(), 2)));
+    }
+
+    public function testFindAllVerticesInGroup()
+    {
+        $graph = new Graph();
+        $group1 = $graph->createGroup(1);
+        $vertex1 = $graph->createVertex(1)->setGroup($group1);
+        $vertex2 = $graph->createVertex(2)->setGroup($group1);
+        $group2 = $graph->createGroup(2);
+        $vertex3 = $graph->createVertex(3)->setGroup($group2);
+
+        $this->assertEquals(
+            array(
+                $vertex1,
+                $vertex2
+            ),
+            $group1->getVerticesInGroup()
+        );
+
+        $this->assertEquals(
+            array(
+                $vertex3
+            ),
+            $group2->getVerticesInGroup()
+        );
+    }
+
+    protected function createAttributeAware()
+    {
+        return new Group(new Graph(), 1);
+    }
+}
diff --git a/tests/Set/BaseVerticesTest.php b/tests/Set/BaseVerticesTest.php
index 06b0a3ac..df3761e0 100644
--- a/tests/Set/BaseVerticesTest.php
+++ b/tests/Set/BaseVerticesTest.php
@@ -198,26 +198,26 @@ public function returnTrue(Vertex $vertex)
     public function testOrderByGroup()
     {
         $graph = new Graph();
-        $graph->createVertex()->setGroup(1);
-        $graph->createVertex()->setGroup(100);
-        $graph->createVertex()->setGroup(5);
-        $graph->createVertex()->setGroup(100);
-        $graph->createVertex()->setGroup(100);
-        $graph->createVertex()->setGroup(2);
-        $biggest = $graph->createVertex()->setGroup(200);
+        $graph->createVertex()->setGroup($graph->createGroup(1));
+        $graph->createVertex()->setGroup($graph->createGroup(100));
+        $graph->createVertex()->setGroup($graph->createGroup(5));
+        $graph->createVertex()->setGroup($graph->createGroup(100, true));
+        $graph->createVertex()->setGroup($graph->createGroup(100, true));
+        $graph->createVertex()->setGroup($graph->createGroup(2));
+        $biggest = $graph->createVertex()->setGroup($graph->createGroup(200));
 
         $vertices = $graph->getVertices();
         $verticesOrdered = $vertices->getVerticesOrder(Vertices::ORDER_GROUP);
 
         $this->assertInstanceOf('Fhaculty\Graph\Set\Vertices', $verticesOrdered);
-        $this->assertEquals(1, $verticesOrdered->getVertexFirst()->getGroup());
-        $this->assertEquals(200, $verticesOrdered->getVertexLast()->getGroup());
+        $this->assertEquals(1, $verticesOrdered->getVertexFirst()->getGroup()->getId());
+        $this->assertEquals(200, $verticesOrdered->getVertexLast()->getGroup()->getId());
 
         $this->assertSame($biggest, $verticesOrdered->getVertexLast());
         $this->assertSame($biggest, $vertices->getVertexOrder(Vertices::ORDER_GROUP, true));
 
         $sumgroups = function(Vertex $vertex) {
-            return $vertex->getGroup();
+            return $vertex->getGroup()->getId();
         };
         $this->assertSame(508, $vertices->getSumCallback($sumgroups));
         $this->assertSame(508, $verticesOrdered->getSumCallback($sumgroups));
diff --git a/tests/VertexTest.php b/tests/VertexTest.php
index 69103e39..e0700b75 100644
--- a/tests/VertexTest.php
+++ b/tests/VertexTest.php
@@ -8,6 +8,16 @@
 
 class VertexTest extends AbstractAttributeAwareTest
 {
+    /**
+     * @var Graph
+     */
+    private $graph;
+
+    /**
+     * @var Vertex
+     */
+    private $vertex;
+
     public function setUp()
     {
         $this->graph = new Graph();
@@ -91,16 +101,8 @@ public function testBalanceInvalid()
 
     public function testGroup()
     {
-        $this->vertex->setGroup(2);
-        $this->assertEquals(2, $this->vertex->getGroup());
-    }
-
-    /**
-     * @expectedException InvalidArgumentException
-     */
-    public function testGroupInvalid()
-    {
-        $this->vertex->setGroup("3");
+        $this->vertex->setGroup($this->graph->createGroup(2));
+        $this->assertEquals(2, $this->vertex->getGroup()->getId());
     }
 
     /**