diff --git a/matrix_common/versionstring.py b/matrix_common/versionstring.py
new file mode 100644
index 0000000..31bc56c
--- /dev/null
+++ b/matrix_common/versionstring.py
@@ -0,0 +1,93 @@
+# Copyright 2016 OpenMarket Ltd
+# Copyright 2021-2022 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import functools
+import logging
+import subprocess
+
+try:
+    from importlib.metadata import distribution
+except ImportError:
+    from importlib_metadata import distribution  # type: ignore
+
+__all__ = ["get_distribution_version_string"]
+
+logger = logging.getLogger(__name__)
+
+
+@functools.lru_cache()
+def get_distribution_version_string(distribution_name: str) -> str:
+    """Calculate a git-aware version string for a distribution package.
+
+    A "distribution package" is a thing that you can e.g. install and manage with pip.
+    It can contain modules, an "import package" of multiple modules, and arbitrary
+    resource data. See the glossary at
+
+        https://packaging.python.org/en/latest/glossary/#term-Distribution-Package
+
+    for all your taxonomic needs. Often a distribution package contains exactly import
+    package---possibly with _different_ names. For example, one can install the
+    "matrix-sydent" distribution package from PyPI using pip, and doing so makes the
+    "sydent" import package available to import.
+
+    Args:
+        distribution_name: The name of the distribution package to check the version of
+
+    Raises:
+        importlib.metadata.PackageNotFoundError if the given distribution name doesn't
+        exist.
+
+    Returns:
+        The module version, possibly with git version information included.
+    """
+
+    dist = distribution(distribution_name)
+    version_string = dist.version
+    cwd = dist.locate_file(".")
+
+    try:
+
+        def _run_git_command(prefix: str, *params: str) -> str:
+            try:
+                result = (
+                    subprocess.check_output(
+                        ["git", *params], stderr=subprocess.DEVNULL, cwd=cwd
+                    )
+                    .strip()
+                    .decode("ascii")
+                )
+                return prefix + result
+            except (subprocess.CalledProcessError, FileNotFoundError):
+                return ""
+
+        git_branch = _run_git_command("b=", "rev-parse", "--abbrev-ref", "HEAD")
+        git_tag = _run_git_command("t=", "describe", "--exact-match")
+        git_commit = _run_git_command("", "rev-parse", "--short", "HEAD")
+
+        dirty_string = "-this_is_a_dirty_checkout"
+        is_dirty = _run_git_command("", "describe", "--dirty=" + dirty_string).endswith(
+            dirty_string
+        )
+        git_dirty = "dirty" if is_dirty else ""
+
+        if git_branch or git_tag or git_commit or git_dirty:
+            git_version = ",".join(
+                s for s in (git_branch, git_tag, git_commit, git_dirty) if s
+            )
+
+            version_string = f"{version_string} ({git_version})"
+    except Exception as e:
+        logger.info("Failed to check for git repository: %s", e)
+
+    return version_string
diff --git a/mypy.ini b/mypy.ini
index be0671c..b76feba 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -1,2 +1,3 @@
 [mypy]
 strict = true
+warn_unused_ignores = false
\ No newline at end of file
diff --git a/setup.cfg b/setup.cfg
index d54b7a4..2e64e90 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -16,6 +16,7 @@ packages =
 python_requires = >= 3.6
 install_requires =
   attrs
+  importlib_metadata >= 1.4; python_version < '3.8'
 
 
 [options.package_data]
diff --git a/tests/test_versionstring.py b/tests/test_versionstring.py
new file mode 100644
index 0000000..a30ae0a
--- /dev/null
+++ b/tests/test_versionstring.py
@@ -0,0 +1,27 @@
+#  Copyright 2022 The Matrix.org Foundation C.I.C.
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+from unittest import TestCase
+
+from matrix_common.versionstring import get_distribution_version_string
+
+
+class TestVersionString(TestCase):
+    def test_our_own_version_string(self) -> None:
+        """Sanity check that we get the version string for our own package.
+
+        Check that it's a nonempty string.
+        """
+        version = get_distribution_version_string("matrix-common")
+        self.assertIsInstance(version, str)
+        self.assertTrue(version)