diff --git a/docs/extensiondev.rst b/docs/extensiondev.rst
index b1928798..f2c54847 100644
--- a/docs/extensiondev.rst
+++ b/docs/extensiondev.rst
@@ -265,13 +265,13 @@ meaningful defaults blank, like ``username`` and ``password``.
         # You will typically only implement one of the next three methods
         # in a single extension.
 
-        def get_frontend_class(self):
+        def get_frontend_classes(self):
             from .frontend import SoundspotFrontend
-            return SoundspotFrontend
+            return [SoundspotFrontend]
 
-        def get_backend_class(self):
+        def get_backend_classes(self):
             from .backend import SoundspotBackend
-            return SoundspotBackend
+            return [SoundspotBackend]
 
         def register_gstreamer_elements(self):
             from .mixer import SoundspotMixer
diff --git a/mopidy/exceptions.py b/mopidy/exceptions.py
index b8d183fb..00c19e9e 100644
--- a/mopidy/exceptions.py
+++ b/mopidy/exceptions.py
@@ -22,3 +22,7 @@ class SettingsError(MopidyException):
 
 class OptionalDependencyError(MopidyException):
     pass
+
+
+class ExtensionError(MopidyException):
+    pass
diff --git a/mopidy/ext.py b/mopidy/ext.py
new file mode 100644
index 00000000..6cc35139
--- /dev/null
+++ b/mopidy/ext.py
@@ -0,0 +1,27 @@
+from __future__ import unicode_literals
+
+
+class Extension(object):
+
+    name = None
+    version = None
+
+    def get_default_config(self):
+        raise NotImplementedError(
+            'Add at least a config section with "enabled = true"')
+
+    def validate_config(self, config):
+        raise NotImplementedError(
+            'You must explicitly pass config validation if not needed')
+
+    def validate_environment(self):
+        pass
+
+    def get_frontend_classes(self):
+        return []
+
+    def get_backend_classes(self):
+        return []
+
+    def register_gstreamer_elements(self):
+        pass
diff --git a/tests/exceptions_test.py b/tests/exceptions_test.py
new file mode 100644
index 00000000..2bc838d7
--- /dev/null
+++ b/tests/exceptions_test.py
@@ -0,0 +1,25 @@
+from __future__ import unicode_literals
+
+from mopidy import exceptions
+
+from tests import unittest
+
+
+class ExceptionsTest(unittest.TestCase):
+    def test_exception_can_include_message_string(self):
+        exc = exceptions.MopidyException('foo')
+
+        self.assertEqual(exc.message, 'foo')
+        self.assertEqual(str(exc), 'foo')
+
+    def test_settings_error_is_a_mopidy_exception(self):
+        self.assert_(issubclass(
+            exceptions.SettingsError, exceptions.MopidyException))
+
+    def test_optional_dependency_error_is_a_mopidy_exception(self):
+        self.assert_(issubclass(
+            exceptions.OptionalDependencyError, exceptions.MopidyException))
+
+    def test_extension_error_is_a_mopidy_exception(self):
+        self.assert_(issubclass(
+            exceptions.ExtensionError, exceptions.MopidyException))
diff --git a/tests/ext_test.py b/tests/ext_test.py
new file mode 100644
index 00000000..ac238ca5
--- /dev/null
+++ b/tests/ext_test.py
@@ -0,0 +1,34 @@
+from __future__ import unicode_literals
+
+from mopidy.ext import Extension
+
+from tests import unittest
+
+
+class ExtensionTest(unittest.TestCase):
+    def setUp(self):
+        self.ext = Extension()
+
+    def test_name_is_none(self):
+        self.assertIsNone(self.ext.name)
+
+    def test_version_is_none(self):
+        self.assertIsNone(self.ext.version)
+
+    def test_get_default_config_raises_not_implemented(self):
+        self.assertRaises(NotImplementedError, self.ext.get_default_config)
+
+    def test_validate_config_raises_not_implemented(self):
+        self.assertRaises(NotImplementedError, self.ext.validate_config, None)
+
+    def test_validate_environment_does_nothing_by_default(self):
+        self.assertIsNone(self.ext.validate_environment())
+
+    def test_get_frontend_classes_returns_an_empty_list(self):
+        self.assertListEqual(self.ext.get_frontend_classes(), [])
+
+    def test_get_backend_classes_returns_an_empty_list(self):
+        self.assertListEqual(self.ext.get_backend_classes(), [])
+
+    def test_register_gstreamer_elements_does_nothing_by_default(self):
+        self.assertIsNone(self.ext.register_gstreamer_elements())