diff --git a/backbone.js b/backbone.js
index a0fb826ac..41ee2aa1b 100644
--- a/backbone.js
+++ b/backbone.js
@@ -68,54 +68,6 @@
   // form param named `model`.
   Backbone.emulateJSON = false;
 
-  // Proxy Backbone class methods to Underscore functions, wrapping the model's
-  // `attributes` object or collection's `models` array behind the scenes.
-  //
-  // collection.filter(function(model) { return model.get('age') > 10 });
-  // collection.each(this.addView);
-  //
-  // `Function#apply` can be slow so we use the method's arg count, if we know it.
-  var addMethod = function(length, method, attribute) {
-    switch (length) {
-      case 1: return function() {
-        return _[method](this[attribute]);
-      };
-      case 2: return function(value) {
-        return _[method](this[attribute], value);
-      };
-      case 3: return function(iteratee, context) {
-        return _[method](this[attribute], cb(iteratee, this), context);
-      };
-      case 4: return function(iteratee, defaultVal, context) {
-        return _[method](this[attribute], cb(iteratee, this), defaultVal, context);
-      };
-      default: return function() {
-        var args = slice.call(arguments);
-        args.unshift(this[attribute]);
-        return _[method].apply(_, args);
-      };
-    }
-  };
-  var addUnderscoreMethods = function(Class, methods, attribute) {
-    _.each(methods, function(length, method) {
-      if (_[method]) Class.prototype[method] = addMethod(length, method, attribute);
-    });
-  };
-
-  // Support `collection.sortBy('attr')` and `collection.findWhere({id: 1})`.
-  var cb = function(iteratee, instance) {
-    if (_.isFunction(iteratee)) return iteratee;
-    if (_.isObject(iteratee) && !instance._isModel(iteratee)) return modelMatcher(iteratee);
-    if (_.isString(iteratee)) return function(model) { return model.get(iteratee); };
-    return iteratee;
-  };
-  var modelMatcher = function(attrs) {
-    var matcher = _.matches(attrs);
-    return function(model) {
-      return matcher(model.attributes);
-    };
-  };
-
   // Backbone.Events
   // ---------------
 
@@ -790,14 +742,6 @@
 
   });
 
-  // Underscore methods that we want to implement on the Model, mapped to the
-  // number of arguments they take.
-  var modelMethods = {keys: 1, values: 1, pairs: 1, invert: 1, pick: 0,
-      omit: 0, chain: 1, isEmpty: 1};
-
-  // Mix in each Underscore method as a proxy to `Model#attributes`.
-  addUnderscoreMethods(Model, modelMethods, 'attributes');
-
   // Backbone.Collection
   // -------------------
 
@@ -1335,21 +1279,6 @@
     return {value: void 0, done: true};
   };
 
-  // Underscore methods that we want to implement on the Collection.
-  // 90% of the core usefulness of Backbone Collections is actually implemented
-  // right here:
-  var collectionMethods = {forEach: 3, each: 3, map: 3, collect: 3, reduce: 0,
-      foldl: 0, inject: 0, reduceRight: 0, foldr: 0, find: 3, detect: 3, filter: 3,
-      select: 3, reject: 3, every: 3, all: 3, some: 3, any: 3, include: 3, includes: 3,
-      contains: 3, invoke: 0, max: 3, min: 3, toArray: 1, size: 1, first: 3,
-      head: 3, take: 3, initial: 3, rest: 3, tail: 3, drop: 3, last: 3,
-      without: 0, difference: 0, indexOf: 3, shuffle: 1, lastIndexOf: 3,
-      isEmpty: 1, chain: 1, sample: 3, partition: 3, groupBy: 3, countBy: 3,
-      sortBy: 3, indexBy: 3, findIndex: 3, findLastIndex: 3};
-
-  // Mix in each Underscore method as a proxy to `Collection#models`.
-  addUnderscoreMethods(Collection, collectionMethods, 'models');
-
   // Backbone.View
   // -------------
 
@@ -1518,6 +1447,94 @@
 
   });
 
+  // Proxy Backbone class methods to Underscore functions, wrapping the model's
+  // `attributes` object or collection's `models` array behind the scenes.
+  //
+  // collection.filter(function(model) { return model.get('age') > 10 });
+  // collection.each(this.addView);
+  //
+  // `Function#apply` can be slow so we use the method's arg count, if we know it.
+  var addMethod = function(base, length, method, attribute) {
+    switch (length) {
+      case 1: return function() {
+        return base[method](this[attribute]);
+      };
+      case 2: return function(value) {
+        return base[method](this[attribute], value);
+      };
+      case 3: return function(iteratee, context) {
+        return base[method](this[attribute], cb(iteratee, this), context);
+      };
+      case 4: return function(iteratee, defaultVal, context) {
+        return base[method](this[attribute], cb(iteratee, this), defaultVal, context);
+      };
+      default: return function() {
+        var args = slice.call(arguments);
+        args.unshift(this[attribute]);
+        return base[method].apply(base, args);
+      };
+    }
+  };
+
+  var addUnderscoreMethods = function(Class, base, methods, attribute) {
+    _.each(methods, function(length, method) {
+      if (base[method]) Class.prototype[method] = addMethod(base, length, method, attribute);
+    });
+  };
+
+  // Support `collection.sortBy('attr')` and `collection.findWhere({id: 1})`.
+  var cb = function(iteratee, instance) {
+    if (_.isFunction(iteratee)) return iteratee;
+    if (_.isObject(iteratee) && !instance._isModel(iteratee)) return modelMatcher(iteratee);
+    if (_.isString(iteratee)) return function(model) { return model.get(iteratee); };
+    return iteratee;
+  };
+  var modelMatcher = function(attrs) {
+    var matcher = _.matches(attrs);
+    return function(model) {
+      return matcher(model.attributes);
+    };
+  };
+
+  // Underscore methods that we want to implement on the Collection.
+  // 90% of the core usefulness of Backbone Collections is actually implemented
+  // right here:
+  var collectionMethods = {forEach: 3, each: 3, map: 3, collect: 3, reduce: 0,
+      foldl: 0, inject: 0, reduceRight: 0, foldr: 0, find: 3, detect: 3, filter: 3,
+      select: 3, reject: 3, every: 3, all: 3, some: 3, any: 3, include: 3, includes: 3,
+      contains: 3, invoke: 0, max: 3, min: 3, toArray: 1, size: 1, first: 3,
+      head: 3, take: 3, initial: 3, rest: 3, tail: 3, drop: 3, last: 3,
+      without: 0, difference: 0, indexOf: 3, shuffle: 1, lastIndexOf: 3,
+      isEmpty: 1, chain: 1, sample: 3, partition: 3, groupBy: 3, countBy: 3,
+      sortBy: 3, indexBy: 3, findIndex: 3, findLastIndex: 3};
+
+
+  // Underscore methods that we want to implement on the Model, mapped to the
+  // number of arguments they take.
+  var modelMethods = {keys: 1, values: 1, pairs: 1, invert: 1, pick: 0,
+      omit: 0, chain: 1, isEmpty: 1};
+
+  // Mix in each Underscore method as a proxy to `Collection#models`.
+
+  _.each([
+    [Collection, collectionMethods, 'models'],
+    [Model, modelMethods, 'attributes']
+  ], function(config) {
+    var Base = config[0],
+        methods = config[1],
+        attribute = config[2];
+
+    Base.mixin = function(obj) {
+      var mappings = _.reduce(_.functions(obj), function(memo, name) {
+        memo[name] = 0;
+        return memo;
+      }, {});
+      addUnderscoreMethods(Base, obj, mappings, attribute);
+    };
+
+    addUnderscoreMethods(Base, _, methods, attribute);
+  });
+
   // Backbone.sync
   // -------------
 
diff --git a/test/collection.js b/test/collection.js
index 467b4581c..139eb9961 100644
--- a/test/collection.js
+++ b/test/collection.js
@@ -711,6 +711,27 @@
     assert.equal(coll.findWhere({a: 4}), void 0);
   });
 
+  QUnit.test('mixin', function(assert) {
+    Backbone.Collection.mixin({
+      sum: function(models, iteratee) {
+        return _.reduce(models, function(s, m) {
+          return s + iteratee(m);
+        }, 0);
+      }
+    });
+
+    var coll = new Backbone.Collection([
+      {a: 1},
+      {a: 1, b: 2},
+      {a: 2, b: 2},
+      {a: 3}
+    ]);
+
+    assert.equal(coll.sum(function(m) {
+      return m.get('a');
+    }), 7);
+  });
+
   QUnit.test('Underscore methods', function(assert) {
     assert.expect(21);
     assert.equal(col.map(function(model){ return model.get('label'); }).join(' '), 'a b c d');
diff --git a/test/model.js b/test/model.js
index 440047fef..b3092df7f 100644
--- a/test/model.js
+++ b/test/model.js
@@ -1395,6 +1395,28 @@
     assert.ok(!model.set('valid', false, {validate: true}));
   });
 
+  QUnit.test('mixin', function(assert) {
+    Backbone.Model.mixin({
+      isEqual: function(model1, model2) {
+        return _.isEqual(model1, model2.attributes);
+      }
+    });
+
+    var model1 = new Backbone.Model({
+      a: {b: 2}, c: 3
+    });
+    var model2 = new Backbone.Model({
+      a: {b: 2}, c: 3
+    });
+    var model3 = new Backbone.Model({
+      a: {b: 4}, c: 3
+    });
+
+    assert.equal(model1.isEqual(model2), true);
+    assert.equal(model1.isEqual(model3), false);
+  });
+
+
   QUnit.test('#1179 - isValid returns true in the absence of validate.', function(assert) {
     assert.expect(1);
     var model = new Backbone.Model();