diff --git a/setup.py b/setup.py
index 65a2dff..3591324 100644
--- a/setup.py
+++ b/setup.py
@@ -1,14 +1,39 @@
 #!/usr/bin/env python
 
 from io import open
+from setuptools import find_packages, setup
 import os
-from setuptools import setup, find_packages
+import re
+import subprocess
+
+
+"""
+Use `git tag 1.0.0` to tag a release; `python setup.py --version`
+to update the  _version.py file.
+"""
 
 
 def get_version(prefix):
-    import re
-    with open(os.path.join(prefix, '__init__.py')) as fd:
-        metadata = dict(re.findall("__([a-z]+)__ = '([^']+)'", fd.read()))
+    if os.path.exists('.git'):
+        parts = subprocess.check_output(['git', 'describe', '--tags']).decode().strip().split('-')
+        if len(parts) == 3:
+            version = '{}.{}+{}'.format(*parts)
+        else:
+            version = parts[0]
+        version_py = "__version__ = '{}'".format(version)
+        _version = os.path.join(prefix, '_version.py')
+        if not os.path.exists(_version) or open(_version).read().strip() != version_py:
+            with open(_version, 'w') as fd:
+                fd.write(version_py)
+        return version
+    else:
+        for f in ('_version.py', '__init__.py'):
+            f = os.path.join(prefix, f)
+            if os.path.exists(f):
+                with open(f) as fd:
+                    metadata = dict(re.findall("__([a-z]+)__ = '([^']+)'", fd.read()))
+                if 'version' in metadata:
+                    break
     return metadata['version']
 
 
diff --git a/shared/markup/__init__.py b/shared/markup/__init__.py
index 5a6f84c..54bc885 100644
--- a/shared/markup/__init__.py
+++ b/shared/markup/__init__.py
@@ -1 +1,4 @@
-__version__ = '0.5'
+try:
+    from ._version import __version__
+except ImportError:
+    pass