diff --git a/mopidy/core/library.py b/mopidy/core/library.py
index e4be7ce8..29b2e797 100644
--- a/mopidy/core/library.py
+++ b/mopidy/core/library.py
@@ -20,6 +20,9 @@ class LibraryController(object):
         """
         Search the library for tracks where ``field`` is ``values``.
 
+        If the query is empty, and the backend can support it, all available
+        tracks are returned.
+
         Examples::
 
             # Returns results matching 'a'
@@ -80,6 +83,9 @@ class LibraryController(object):
         """
         Search the library for tracks where ``field`` contains ``values``.
 
+        If the query is empty, and the backend can support it, all available
+        tracks are returned.
+
         Examples::
 
             # Returns results matching 'a'