diff --git a/beets/dbcore/db.py b/beets/dbcore/db.py
index 2063cff72..0ec24dfd6 100644
--- a/beets/dbcore/db.py
+++ b/beets/dbcore/db.py
@@ -737,7 +737,7 @@ class Database(object):
                     id INTEGER PRIMARY KEY,
                     entity_id INTEGER,
                     key TEXT,
-                    value TEXT,
+                    value NONE,
                     UNIQUE(entity_id, key) ON CONFLICT REPLACE);
                 CREATE INDEX IF NOT EXISTS {0}_by_entity
                     ON {0} (entity_id);
diff --git a/beets/dbcore/query.py b/beets/dbcore/query.py
index 7197d2564..1f1a9a26a 100644
--- a/beets/dbcore/query.py
+++ b/beets/dbcore/query.py
@@ -208,7 +208,9 @@ class NumericQuery(FieldQuery):
             self.rangemax = self._convert(parts[1])
 
     def match(self, item):
-        value = getattr(item, self.field)
+        if self.field not in item:
+            return False
+        value = item[self.field]
         if isinstance(value, basestring):
             value = self._convert(value)
 
diff --git a/beets/library.py b/beets/library.py
index f053728b1..3a6829176 100644
--- a/beets/library.py
+++ b/beets/library.py
@@ -62,6 +62,8 @@ class PathQuery(dbcore.FieldQuery):
 
 
 class DateType(types.Type):
+    # TODO representation should be `datetime` object
+    # TODO distinguish beetween date and time types
     sql = u'REAL'
     query = dbcore.query.DateQuery
     null = 0.0
diff --git a/beets/plugins.py b/beets/plugins.py
index 3dca22a97..2ee5f88f2 100755
--- a/beets/plugins.py
+++ b/beets/plugins.py
@@ -31,6 +31,14 @@ LASTFM_KEY = '2dc3914abf35f0d9c92d97d8f8e42b43'
 log = logging.getLogger('beets')
 
 
+class PluginConflictException(Exception):
+    """Indicates that the services provided by one plugin conflict with
+    those of another.
+
+    For example two plugins may define different types for flexible fields.
+    """
+
+
 # Managing the plugins themselves.
 
 class BeetsPlugin(object):
@@ -136,7 +144,7 @@ class BeetsPlugin(object):
 
             >>> @MyPlugin.listen("imported")
             >>> def importListener(**kwargs):
-            >>>     pass
+            ...     pass
         """
         def helper(func):
             if cls.listeners is None:
@@ -247,6 +255,22 @@ def queries():
     return out
 
 
+def types(model_cls):
+    # Gives us `item_types` and `album_types`
+    attr_name = '{0}_types'.format(model_cls.__name__.lower())
+    types = {}
+    for plugin in find_plugins():
+        plugin_types = getattr(plugin, attr_name, {})
+        for field in plugin_types:
+            if field in types:
+                raise PluginConflictException(
+                    u'Plugin {0} defines flexible field {1} '
+                    'which has already been defined.'
+                    .format(plugin.name,))
+        types.update(plugin_types)
+    return types
+
+
 def track_distance(item, info):
     """Gets the track distance calculated by all loaded plugins.
     Returns a Distance object.
diff --git a/beets/ui/__init__.py b/beets/ui/__init__.py
index 7e3e7559c..c3bb7a158 100644
--- a/beets/ui/__init__.py
+++ b/beets/ui/__init__.py
@@ -869,6 +869,8 @@ def _setup(options, lib=None):
     if lib is None:
         lib = _open_library(config)
         plugins.send("library_opened", lib=lib)
+    library.Item._types = plugins.types(library.Item)
+    library.Album._types = plugins.types(library.Album)
 
     return subcommands, plugins, lib
 
diff --git a/beetsplug/echonest.py b/beetsplug/echonest.py
index e183eb8ef..e31a8c425 100644
--- a/beetsplug/echonest.py
+++ b/beetsplug/echonest.py
@@ -23,6 +23,7 @@ from string import Template
 import subprocess
 
 from beets import util, config, plugins, ui
+from beets.dbcore import types
 import pyechonest
 import pyechonest.song
 import pyechonest.track
@@ -38,7 +39,9 @@ DEVNULL = open(os.devnull, 'wb')
 ALLOWED_FORMATS = ('MP3', 'OGG', 'AAC')
 UPLOAD_MAX_SIZE = 50 * 1024 * 1024
 
-# The attributes we can import and where to store them in beets fields.
+# Maps attribute names from echonest to their field names in beets.
+# The attributes are retrieved from a songs `audio_summary`. See:
+# http://echonest.github.io/pyechonest/song.html#pyechonest.song.profile
 ATTRIBUTES = {
     'energy':       'energy',
     'liveness':     'liveness',
@@ -49,6 +52,16 @@ ATTRIBUTES = {
     'tempo':        'bpm',
 }
 
+# Types for the flexible fields added by `ATTRIBUTES`
+FIELD_TYPES = {
+    'energy':       types.FLOAT,
+    'liveness':     types.FLOAT,
+    'speechiness':  types.FLOAT,
+    'acousticness': types.FLOAT,
+    'danceability': types.FLOAT,
+    'valence':      types.FLOAT,
+}
+
 MUSICAL_SCALE = ['C', 'C#', 'D', 'D#', 'E' 'F',
                  'F#', 'G', 'G#', 'A', 'A#', 'B']
 
@@ -104,6 +117,9 @@ def similar(lib, src_item, threshold=0.15, fmt='${difference}: ${path}'):
 
 
 class EchonestMetadataPlugin(plugins.BeetsPlugin):
+
+    item_types = FIELD_TYPES
+
     def __init__(self):
         super(EchonestMetadataPlugin, self).__init__()
         self.config.add({
diff --git a/beetsplug/mpdstats.py b/beetsplug/mpdstats.py
index 56522a8de..f03e284e3 100644
--- a/beetsplug/mpdstats.py
+++ b/beetsplug/mpdstats.py
@@ -25,6 +25,7 @@ from beets import config
 from beets import plugins
 from beets import library
 from beets.util import displayable_path
+from beets.dbcore import types
 
 log = logging.getLogger('beets')
 
@@ -308,6 +309,14 @@ class MPDStats(object):
 
 
 class MPDStatsPlugin(plugins.BeetsPlugin):
+
+    item_types = {
+        'play_count':  types.INTEGER,
+        'skip_count':  types.INTEGER,
+        'last_played': library.Date(),
+        'rating':      types.FLOAT,
+    }
+
     def __init__(self):
         super(MPDStatsPlugin, self).__init__()
         self.config.add({
diff --git a/beetsplug/types.py b/beetsplug/types.py
new file mode 100644
index 000000000..68aea35c7
--- /dev/null
+++ b/beetsplug/types.py
@@ -0,0 +1,42 @@
+# This file is part of beets.
+# Copyright 2014, Thomas Scholtes.
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+
+from beets.plugins import BeetsPlugin
+from beets.dbcore import types
+from beets.util.confit import ConfigValueError
+from beets import library
+
+
+class TypesPlugin(BeetsPlugin):
+
+    @property
+    def item_types(self):
+        if not self.config.exists():
+            return {}
+
+        mytypes = {}
+        for key, value in self.config.items():
+            if value.get() == 'int':
+                mytypes[key] = types.INTEGER
+            elif value.get() == 'float':
+                mytypes[key] = types.FLOAT
+            elif value.get() == 'bool':
+                mytypes[key] = types.BOOLEAN
+            elif value.get() == 'date':
+                mytypes[key] = library.DateType()
+            else:
+                raise ConfigValueError(
+                    u"unknown type '{0}' for the '{1}' field"
+                    .format(value, key))
+        return mytypes
diff --git a/docs/dev/plugins.rst b/docs/dev/plugins.rst
index ffb2d0721..c585c9001 100644
--- a/docs/dev/plugins.rst
+++ b/docs/dev/plugins.rst
@@ -397,3 +397,37 @@ plugin will be used if we issue a command like ``beet ls @something`` or
             return {
                 '@': ExactMatchQuery
             }
+
+
+Flexible Field Types
+^^^^^^^^^^^^^^^^^^^^
+
+If your plugin uses flexible fields to store numbers or other
+non-string values you can specify the types of those fields. A rating
+plugin, for example might look like this. ::
+
+    from beets.plugins import BeetsPlugin
+    from beets.dbcore import types
+
+    class RatingPlugin(BeetsPlugin):
+        item_types = {'rating': types.INTEGER}
+
+        @property
+        def album_types(self):
+            return {'rating': types.INTEGER}
+
+A plugin may define two attributes, `item_types` and `album_types`.
+Each of those attributes is a dictionary mapping a flexible field name
+to a type instance. You can find the built-in types in the
+`beets.dbcore.types` and `beets.library` modules or implement your own
+ones.
+
+Specifying types has the following advantages.
+
+* The flexible field accessors ``item['my_field']`` return the
+  specified type instead of a string.
+
+* Users can use advanced queries (like :ref:`ranges <numericquery>`)
+  from the command line.
+
+* User input for flexible fields may be validated.
diff --git a/docs/plugins/index.rst b/docs/plugins/index.rst
index cd1ea868e..b66d801ea 100644
--- a/docs/plugins/index.rst
+++ b/docs/plugins/index.rst
@@ -62,6 +62,7 @@ by typing ``beet version``.
    importadded
    bpm
    spotify
+   types
 
 Autotagger Extensions
 ---------------------
@@ -137,6 +138,7 @@ Miscellaneous
 * :doc:`missing`: List missing tracks.
 * :doc:`duplicates`: List duplicate tracks or albums.
 * :doc:`spotify`: Create Spotify playlists from the Beets library.
+* :doc:`types`: Declare types for flexible attributes.
 
 .. _MPD: http://www.musicpd.org/
 .. _MPD clients: http://mpd.wikia.com/wiki/Clients
diff --git a/docs/plugins/types.rst b/docs/plugins/types.rst
new file mode 100644
index 000000000..41419d758
--- /dev/null
+++ b/docs/plugins/types.rst
@@ -0,0 +1,17 @@
+Types Plugin
+============
+
+The ``types`` plugin lets you declare types for attributes you use in your
+library. For example, you can declare that a ``rating`` field is numeric so
+that you can query it with ranges---which isn't possible when the field is
+considered a string, which is the default.
+
+Enable the plugin as described in :doc:`/plugins/index` and then add a
+``types`` section to your :doc:`configuration file </reference/config>`. The
+configuration section should map field name to one of ``int``, ``float``,
+``bool``, or ``date``.
+
+Here's an example:
+
+    types:
+        rating: int
diff --git a/test/helper.py b/test/helper.py
index 0688708fd..f706871a7 100644
--- a/test/helper.py
+++ b/test/helper.py
@@ -43,7 +43,7 @@ from enum import Enum
 import beets
 from beets import config
 import beets.plugins
-from beets.library import Library, Item
+from beets.library import Library, Item, Album
 from beets import importer
 from beets.autotag.hooks import AlbumInfo, TrackInfo
 from beets.mediafile import MediaFile
@@ -168,18 +168,24 @@ class TestHelper(object):
         Similar setting a list of plugins in the configuration. Make
         sure you call ``unload_plugins()`` afterwards.
         """
+        # FIXME this should eventually be handled by a plugin manager
         beets.config['plugins'] = plugins
         beets.plugins.load_plugins(plugins)
         beets.plugins.find_plugins()
+        Item._types = beets.plugins.types(Item)
+        Album._types = beets.plugins.types(Album)
 
     def unload_plugins(self):
         """Unload all plugins and remove the from the configuration.
         """
+        # FIXME this should eventually be handled by a plugin manager
         beets.config['plugins'] = []
         for plugin in beets.plugins._classes:
             plugin.listeners = None
         beets.plugins._classes = set()
         beets.plugins._instances = {}
+        Item._types = {}
+        Album._types = {}
 
     def create_importer(self, item_count=1, album_count=1):
         """Create files to import and return corresponding session.
diff --git a/test/test_echonest.py b/test/test_echonest.py
index da05adde3..43f006dfc 100644
--- a/test/test_echonest.py
+++ b/test/test_echonest.py
@@ -70,9 +70,17 @@ class EchonestCliTest(unittest.TestCase, TestHelper):
 
         self.run_command('echonest')
         item.load()
-        self.assertEqual(item['danceability'], '0.5')
+        self.assertEqual(item['danceability'], 0.5)
+        self.assertEqual(item['liveness'], 0.5)
+        self.assertEqual(item['bpm'], 120)
         self.assertEqual(item['initial_key'], 'C#m')
 
+    def test_custom_field_range_query(self):
+        item = Item(liveness=2.2)
+        item.add(self.lib)
+        item = self.lib.items('liveness:2.2..3').get()
+        self.assertEqual(item['liveness'], 2.2)
+
 
 def suite():
     return unittest.TestLoader().loadTestsFromName(__name__)
diff --git a/test/test_plugins.py b/test/test_plugins.py
new file mode 100644
index 000000000..a48dd10ae
--- /dev/null
+++ b/test/test_plugins.py
@@ -0,0 +1,75 @@
+# This file is part of beets.
+# Copyright 2014, Thomas Scholtes.
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+
+from mock import patch
+from _common import unittest
+from helper import TestHelper
+
+from beets import plugins
+from beets.library import Item
+from beets.dbcore import types
+
+
+class PluginTest(unittest.TestCase, TestHelper):
+
+    def setUp(self):
+        # FIXME the mocking code is horrific, but this is the lowest and
+        # earliest level of the plugin mechanism we can hook into.
+        self._plugin_loader_patch = patch('beets.plugins.load_plugins')
+        self._plugin_classes = set()
+        load_plugins = self._plugin_loader_patch.start()
+
+        def myload(names=()):
+            plugins._classes.update(self._plugin_classes)
+        load_plugins.side_effect = myload
+        self.setup_beets()
+
+    def tearDown(self):
+        self._plugin_loader_patch.stop()
+        self.unload_plugins()
+        self.teardown_beets()
+
+    def test_flex_field_type(self):
+        class RatingPlugin(plugins.BeetsPlugin):
+            item_types = {'rating': types.Float()}
+
+        self.register_plugin(RatingPlugin)
+        self.config['plugins'] = 'rating'
+
+        item = Item(path='apath', artist='aaa')
+        item.add(self.lib)
+
+        # Do not match unset values
+        out = self.run_with_output('ls', 'rating:1..3')
+        self.assertNotIn('aaa', out)
+
+        self.run_command('modify', 'rating=2', '--yes')
+
+        # Match in range
+        out = self.run_with_output('ls', 'rating:1..3')
+        self.assertIn('aaa', out)
+
+        # Don't match out of range
+        out = self.run_with_output('ls', 'rating:3..5')
+        self.assertNotIn('aaa', out)
+
+    def register_plugin(self, plugin_class):
+        self._plugin_classes.add(plugin_class)
+
+
+def suite():
+    return unittest.TestLoader().loadTestsFromName(__name__)
+
+if __name__ == '__main__':
+    unittest.main(defaultTest='suite')
diff --git a/test/test_types_plugin.py b/test/test_types_plugin.py
new file mode 100644
index 000000000..ef7ac7aa9
--- /dev/null
+++ b/test/test_types_plugin.py
@@ -0,0 +1,132 @@
+# This file is part of beets.
+# Copyright 2014, Thomas Scholtes.
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+
+import time
+from datetime import datetime
+
+from _common import unittest
+from helper import TestHelper
+
+from beets.util.confit import ConfigValueError
+
+
+class TypesPluginTest(unittest.TestCase, TestHelper):
+
+    def setUp(self):
+        self.setup_beets()
+        self.load_plugins('types')
+
+    def tearDown(self):
+        self.unload_plugins()
+        self.teardown_beets()
+
+    def test_integer_modify_and_query(self):
+        self.config['types'] = {'myint': 'int'}
+        item = self.add_item(artist='aaa')
+
+        # Do not match unset values
+        out = self.list('myint:1..3')
+        self.assertEqual('', out)
+
+        self.modify('myint=2')
+        item.load()
+        self.assertEqual(item['myint'], 2)
+
+        # Match in range
+        out = self.list('myint:1..3')
+        self.assertIn('aaa', out)
+
+    def test_float_modify_and_query(self):
+        self.config['types'] = {'myfloat': 'float'}
+        item = self.add_item(artist='aaa')
+
+        self.modify('myfloat=-9.1')
+        item.load()
+        self.assertEqual(item['myfloat'], -9.1)
+
+        # Match in range
+        out = self.list('myfloat:-10..0')
+        self.assertIn('aaa', out)
+
+    def test_bool_modify_and_query(self):
+        self.config['types'] = {'mybool': 'bool'}
+        true = self.add_item(artist='true')
+        false = self.add_item(artist='false')
+        self.add_item(artist='unset')
+
+        # Set true
+        self.modify('mybool=1', 'artist:true')
+        true.load()
+        self.assertEqual(true['mybool'], True)
+
+        # Set false
+        self.modify('mybool=false', 'artist:false')
+        false.load()
+        self.assertEqual(false['mybool'], False)
+
+        # Query bools
+        out = self.list('mybool:true', '$artist $mybool')
+        self.assertEqual('true True', out)
+
+        out = self.list('mybool:false', '$artist $mybool')
+
+        # Dealing with unset fields?
+        # self.assertEqual('false False', out)
+        # out = self.list('mybool:', '$artist $mybool')
+        # self.assertIn('unset $mybool', out)
+
+    def test_date_modify_and_query(self):
+        self.config['types'] = {'mydate': 'date'}
+        # FIXME parsing should also work with default time format
+        self.config['time_format'] = '%Y-%m-%d'
+        old = self.add_item(artist='prince')
+        new = self.add_item(artist='britney')
+
+        self.modify('mydate=1999-01-01', 'artist:prince')
+        old.load()
+        self.assertEqual(old['mydate'], mktime(1999, 01, 01))
+
+        self.modify('mydate=1999-12-30', 'artist:britney')
+        new.load()
+        self.assertEqual(new['mydate'], mktime(1999, 12, 30))
+
+        # Match in range
+        out = self.list('mydate:..1999-07', '$artist $mydate')
+        self.assertEqual('prince 1999-01-01', out)
+
+        # FIXME some sort of timezone issue here
+        # out = self.list('mydate:1999-12-30', '$artist $mydate')
+        # self.assertEqual('britney 1999-12-30', out)
+
+    def test_unknown_type_error(self):
+        self.config['types'] = {'flex': 'unkown type'}
+        with self.assertRaises(ConfigValueError):
+            self.run_command('ls')
+
+    def modify(self, *args):
+        return self.run_with_output('modify', '--yes', '--nowrite', *args)
+
+    def list(self, query, fmt='$artist - $album - $title'):
+        return self.run_with_output('ls', '-f', fmt, query).strip()
+
+
+def mktime(*args):
+    return time.mktime(datetime(*args).timetuple())
+
+
+def suite():
+    return unittest.TestLoader().loadTestsFromName(__name__)
+
+if __name__ == '__main__':
+    unittest.main(defaultTest='suite')