diff --git a/docs/api/backends/controllers.rst b/docs/api/backends/controllers.rst
index 28112cf7..20dc2d61 100644
--- a/docs/api/backends/controllers.rst
+++ b/docs/api/backends/controllers.rst
@@ -15,7 +15,6 @@ The backend
 
 .. autoclass:: mopidy.backends.base.Backend
     :members:
-    :undoc-members:
 
 
 Playback controller
@@ -26,7 +25,6 @@ seek.
 
 .. autoclass:: mopidy.backends.base.PlaybackController
     :members:
-    :undoc-members:
 
 
 Mixer controller
@@ -42,7 +40,6 @@ Manages everything related to the currently loaded playlist.
 
 .. autoclass:: mopidy.backends.base.CurrentPlaylistController
     :members:
-    :undoc-members:
 
 
 Stored playlists controller
@@ -52,7 +49,6 @@ Manages stored playlist.
 
 .. autoclass:: mopidy.backends.base.StoredPlaylistsController
     :members:
-    :undoc-members:
 
 
 Library controller
@@ -62,4 +58,3 @@ Manages the music library, e.g. searching for tracks to be added to a playlist.
 
 .. autoclass:: mopidy.backends.base.LibraryController
     :members:
-    :undoc-members:
diff --git a/docs/api/backends/providers.rst b/docs/api/backends/providers.rst
index 903e220b..61e5f68a 100644
--- a/docs/api/backends/providers.rst
+++ b/docs/api/backends/providers.rst
@@ -14,7 +14,6 @@ Playback provider
 
 .. autoclass:: mopidy.backends.base.BasePlaybackProvider
     :members:
-    :undoc-members:
 
 
 Stored playlists provider
@@ -22,7 +21,6 @@ Stored playlists provider
 
 .. autoclass:: mopidy.backends.base.BaseStoredPlaylistsProvider
     :members:
-    :undoc-members:
 
 
 Library provider
@@ -30,7 +28,6 @@ Library provider
 
 .. autoclass:: mopidy.backends.base.BaseLibraryProvider
     :members:
-    :undoc-members:
 
 
 Backend provider implementations
diff --git a/docs/api/frontends.rst b/docs/api/frontends.rst
index 0c1e32a3..792e4bc9 100644
--- a/docs/api/frontends.rst
+++ b/docs/api/frontends.rst
@@ -2,22 +2,26 @@
 Frontend API
 ************
 
-A frontend may do whatever it wants to, including creating threads, opening TCP
-ports and exposing Mopidy for a type of clients.
-
-Frontends got one main limitation: they are restricted to passing messages
-through the ``core_queue`` for all communication with the rest of Mopidy. Thus,
-the frontend API is very small and reveals little of what a frontend may do.
-
-.. warning::
-
-    A stable frontend API is not available yet, as we've only implemented a
-    couple of frontend modules.
-
-.. automodule:: mopidy.frontends.base
-    :synopsis: Base class for frontends
-    :members:
+The following requirements applies to any frontend implementation:
 
+- A frontend MAY do mostly whatever it wants to, including creating threads,
+  opening TCP ports and exposing Mopidy for a group of clients.
+- A frontend MUST implement at least one `Pykka
+  <http://jodal.github.com/pykka/>`_ actor, called the "main actor" from here
+  on.
+- It MAY use additional actors to implement whatever it does, and using actors
+  in frontend implementations is encouraged.
+- The frontend is activated by including its main actor in the
+  :attr:`mopidy.settings.FRONTENDS` setting.
+- The main actor MUST be able to start and stop the frontend when the main
+  actor is started and stopped.
+- The frontend MAY require additional settings to be set for it to
+  work.
+- Such settings MUST be documented.
+- The main actor MUST stop itself if the defined settings are not adequate for
+  the frontend to work properly.
+- Any actor which is part of the frontend MAY implement any listener interface
+  from :mod:`mopidy.listeners` to receive notification of the specified events.
 
 Frontend implementations
 ========================
diff --git a/docs/api/listeners.rst b/docs/api/listeners.rst
new file mode 100644
index 00000000..609dc3c7
--- /dev/null
+++ b/docs/api/listeners.rst
@@ -0,0 +1,7 @@
+************
+Listener API
+************
+
+.. automodule:: mopidy.listeners
+    :synopsis: Listener API
+    :members:
diff --git a/docs/api/mixers.rst b/docs/api/mixers.rst
index 6daa7a4e..2459db8c 100644
--- a/docs/api/mixers.rst
+++ b/docs/api/mixers.rst
@@ -30,7 +30,6 @@ methods as described below.
 .. automodule:: mopidy.mixers.base
     :synopsis: Mixer API
     :members:
-    :undoc-members:
 
 
 Mixer implementations
diff --git a/docs/api/models.rst b/docs/api/models.rst
index ef11547e..5833e58c 100644
--- a/docs/api/models.rst
+++ b/docs/api/models.rst
@@ -25,4 +25,3 @@ Data model API
 .. automodule:: mopidy.models
     :synopsis: Data model API
     :members:
-    :undoc-members:
diff --git a/docs/changes.rst b/docs/changes.rst
index 07212cc7..db03498c 100644
--- a/docs/changes.rst
+++ b/docs/changes.rst
@@ -13,6 +13,9 @@ v0.6.0 (in development)
 - Replace :attr:`mopidy.backends.base.Backend.uri_handlers` with
   :attr:`mopidy.backends.base.Backend.uri_schemes`, which just takes the part
   up to the colon of an URI, and not any prefix.
+- Add Listener API, :mod:`mopidy.listeners`, to be implemented by actors
+  wanting to receive events from the backend. This is a formalization of the
+  ad hoc events the Last.fm scrobbler has already been using for some time.
 
 
 v0.5.0 (2011-06-15)
diff --git a/docs/modules/frontends/mpd.rst b/docs/modules/frontends/mpd.rst
index 6120c2a6..6f69b2a9 100644
--- a/docs/modules/frontends/mpd.rst
+++ b/docs/modules/frontends/mpd.rst
@@ -5,9 +5,8 @@
 .. inheritance-diagram:: mopidy.frontends.mpd
 
 .. automodule:: mopidy.frontends.mpd
-    :synopsis: MPD frontend
+    :synopsis: MPD server frontend
     :members:
-    :undoc-members:
 
 
 MPD server
@@ -18,7 +17,6 @@ MPD server
 .. automodule:: mopidy.frontends.mpd.server
     :synopsis: MPD server
     :members:
-    :undoc-members:
 
 
 MPD session
@@ -29,7 +27,6 @@ MPD session
 .. automodule:: mopidy.frontends.mpd.session
     :synopsis: MPD client session
     :members:
-    :undoc-members:
 
 
 MPD dispatcher
@@ -40,7 +37,6 @@ MPD dispatcher
 .. automodule:: mopidy.frontends.mpd.dispatcher
     :synopsis: MPD request dispatcher
     :members:
-    :undoc-members:
 
 
 MPD protocol
diff --git a/docs/settings.rst b/docs/settings.rst
index f0888670..68adfd55 100644
--- a/docs/settings.rst
+++ b/docs/settings.rst
@@ -151,4 +151,3 @@ Available settings
 .. automodule:: mopidy.settings
     :synopsis: Available settings and their default values
     :members:
-    :undoc-members:
diff --git a/mopidy/backends/base/playback.py b/mopidy/backends/base/playback.py
index 29188f55..e94ddf4d 100644
--- a/mopidy/backends/base/playback.py
+++ b/mopidy/backends/base/playback.py
@@ -4,7 +4,7 @@ import time
 
 from pykka.registry import ActorRegistry
 
-from mopidy.frontends.base import BaseFrontend
+from mopidy.listeners import BackendListener
 
 logger = logging.getLogger('mopidy.backends.base')
 
@@ -486,23 +486,21 @@ class PlaybackController(object):
 
     def _trigger_started_playing_event(self):
         """
-        Notifies frontends that a track has started playing.
+        Notifies implementors of :class:`mopidy.listeners.BackendListener` that
+        a track has started playing.
 
         For internal use only. Should be called by the backend directly after a
         track has started playing.
         """
         if self.current_track is None:
             return
-        frontend_refs = ActorRegistry.get_by_class(BaseFrontend)
-        for frontend_ref in frontend_refs:
-            frontend_ref.send_one_way({
-                'command': 'started_playing',
-                'track': self.current_track,
-            })
+        for listener_ref in ActorRegistry.get_by_class(BackendListener):
+            listener_ref.proxy().started_playing(track=self.current_track)
 
     def _trigger_stopped_playing_event(self):
         """
-        Notifies frontends that a track has stopped playing.
+        Notifies implementors of :class:`mopidy.listeners.BackendListener` that
+        a track has stopped playing.
 
         For internal use only. Should be called by the backend before a track
         is stopped playing, e.g. at the next, previous, and stop actions and at
@@ -510,13 +508,9 @@ class PlaybackController(object):
         """
         if self.current_track is None:
             return
-        frontend_refs = ActorRegistry.get_by_class(BaseFrontend)
-        for frontend_ref in frontend_refs:
-            frontend_ref.send_one_way({
-                'command': 'stopped_playing',
-                'track': self.current_track,
-                'stop_position': self.time_position,
-            })
+        for listener_ref in ActorRegistry.get_by_class(BackendListener):
+            listener_ref.proxy().stopped_playing(
+                track=self.current_track, stop_position=self.time_position)
 
 
 class BasePlaybackProvider(object):
diff --git a/mopidy/backends/spotify/translator.py b/mopidy/backends/spotify/translator.py
index 1bf7e5aa..95287d77 100644
--- a/mopidy/backends/spotify/translator.py
+++ b/mopidy/backends/spotify/translator.py
@@ -4,7 +4,7 @@ import logging
 from spotify import Link, SpotifyError
 
 from mopidy import settings
-from mopidy.backends.spotify import ENCODING, BITRATES
+from mopidy.backends.spotify import ENCODING
 from mopidy.models import Artist, Album, Track, Playlist
 
 logger = logging.getLogger('mopidy.backends.spotify.translator')
@@ -44,7 +44,7 @@ class SpotifyTranslator(object):
             track_no=spotify_track.index(),
             date=date,
             length=spotify_track.duration(),
-            bitrate=BITRATES[settings.SPOTIFY_BITRATE],
+            bitrate=settings.SPOTIFY_BITRATE,
         )
 
     @classmethod
diff --git a/mopidy/frontends/base.py b/mopidy/frontends/base.py
deleted file mode 100644
index 811644b1..00000000
--- a/mopidy/frontends/base.py
+++ /dev/null
@@ -1,5 +0,0 @@
-class BaseFrontend(object):
-    """
-    Base class for frontends.
-    """
-    pass
diff --git a/mopidy/frontends/lastfm.py b/mopidy/frontends/lastfm.py
index 04716c61..33e724c0 100644
--- a/mopidy/frontends/lastfm.py
+++ b/mopidy/frontends/lastfm.py
@@ -10,14 +10,14 @@ except ImportError as import_error:
 from pykka.actor import ThreadingActor
 
 from mopidy import settings, SettingsError
-from mopidy.frontends.base import BaseFrontend
+from mopidy.listeners import BackendListener
 
 logger = logging.getLogger('mopidy.frontends.lastfm')
 
 API_KEY = '2236babefa8ebb3d93ea467560d00d04'
 API_SECRET = '94d9a09c0cd5be955c4afaeaffcaefcd'
 
-class LastfmFrontend(ThreadingActor, BaseFrontend):
+class LastfmFrontend(ThreadingActor, BackendListener):
     """
     Frontend which scrobbles the music you play to your `Last.fm
     <http://www.last.fm>`_ profile.
@@ -57,14 +57,6 @@ class LastfmFrontend(ThreadingActor, BaseFrontend):
             logger.error(u'Error during Last.fm setup: %s', e)
             self.stop()
 
-    def on_receive(self, message):
-        if message.get('command') == 'started_playing':
-            self.started_playing(message['track'])
-        elif message.get('command') == 'stopped_playing':
-            self.stopped_playing(message['track'], message['stop_position'])
-        else:
-            pass # Ignore any other messages
-
     def started_playing(self, track):
         artists = ', '.join([a.name for a in track.artists])
         duration = track.length and track.length // 1000 or 0
diff --git a/mopidy/frontends/mpd/__init__.py b/mopidy/frontends/mpd/__init__.py
index 175aa0ee..f37b2deb 100644
--- a/mopidy/frontends/mpd/__init__.py
+++ b/mopidy/frontends/mpd/__init__.py
@@ -3,13 +3,12 @@ import logging
 
 from pykka.actor import ThreadingActor
 
-from mopidy.frontends.base import BaseFrontend
 from mopidy.frontends.mpd.server import MpdServer
 from mopidy.utils.process import BaseThread
 
 logger = logging.getLogger('mopidy.frontends.mpd')
 
-class MpdFrontend(ThreadingActor, BaseFrontend):
+class MpdFrontend(ThreadingActor):
     """
     The MPD frontend.
 
diff --git a/mopidy/listeners.py b/mopidy/listeners.py
new file mode 100644
index 00000000..f6d1c67e
--- /dev/null
+++ b/mopidy/listeners.py
@@ -0,0 +1,34 @@
+class BackendListener(object):
+    """
+    Marker interface for recipients of events sent by the backend.
+
+    Any Pykka actor that mixes in this class will receive calls to the methods
+    defined here when the corresponding events happen in the backend. This
+    interface is used both for looking up what actors to notify of the events,
+    and for providing default implementations for those listeners that are not
+    interested in all events.
+    """
+
+    def started_playing(self, track):
+        """
+        Called whenever a new track starts playing.
+
+        *MAY* be implemented by actor.
+
+        :param track: the track that just started playing
+        :type track: :class:`mopidy.models.Track`
+        """
+        pass
+
+    def stopped_playing(self, track, stop_position):
+        """
+        Called whenever playback is stopped.
+
+        *MAY* be implemented by actor.
+
+        :param track: the track that was played before playback stopped
+        :type track: :class:`mopidy.models.Track`
+        :param stop_position: the time position when stopped in milliseconds
+        :type stop_position: int
+        """
+        pass
diff --git a/tests/listeners_test.py b/tests/listeners_test.py
new file mode 100644
index 00000000..761aff4f
--- /dev/null
+++ b/tests/listeners_test.py
@@ -0,0 +1,14 @@
+import unittest
+
+from mopidy.listeners import BackendListener
+from mopidy.models import Track
+
+class BackendListenerTest(unittest.TestCase):
+    def setUp(self):
+        self.listener = BackendListener()
+
+    def test_listener_has_default_impl_for_the_started_playing_event(self):
+        self.listener.started_playing(Track())
+
+    def test_listener_has_default_impl_for_the_stopped_playing_event(self):
+        self.listener.stopped_playing(Track(), 0)