diff --git a/backbone.js b/backbone.js
index df6f538e..69ea96dc 100644
--- a/backbone.js
+++ b/backbone.js
@@ -641,7 +641,7 @@
   var methods = ['forEach', 'each', 'map', 'reduce', 'reduceRight', 'find', 'detect',
     'filter', 'select', 'reject', 'every', 'all', 'some', 'any', 'include',
     'contains', 'invoke', 'max', 'min', 'sortBy', 'sortedIndex', 'toArray', 'size',
-    'first', 'rest', 'last', 'without', 'indexOf', 'lastIndexOf', 'isEmpty'];
+    'first', 'rest', 'last', 'without', 'indexOf', 'lastIndexOf', 'isEmpty', 'groupBy'];
 
   // Mix in each Underscore method as a proxy to `Collection#models`.
   _.each(methods, function(method) {
diff --git a/index.html b/index.html
index 1b72816b..2c5e6333 100644
--- a/index.html
+++ b/index.html
@@ -207,7 +207,7 @@
       <li>– <a href="#Collection-constructor">constructor / initialize</a></li>
       <li>– <a href="#Collection-models">models</a></li>
       <li>– <a href="#Collection-toJSON">toJSON</a></li>
-      <li>– <a href="#Collection-Underscore-Methods"><b>Underscore Methods (25)</b></a></li>
+      <li>– <a href="#Collection-Underscore-Methods"><b>Underscore Methods (26)</b></a></li>
       <li>– <a href="#Collection-add">add</a></li>
       <li>– <a href="#Collection-remove">remove</a></li>
       <li>– <a href="#Collection-get">get</a></li>
@@ -1113,9 +1113,9 @@ alert(JSON.stringify(collection));
 </pre>
 
     <p id="Collection-Underscore-Methods">
-      <b class="header">Underscore Methods (25)</b>
+      <b class="header">Underscore Methods (26)</b>
       <br />
-      Backbone proxies to <b>Underscore.js</b> to provide 25 iteration functions
+      Backbone proxies to <b>Underscore.js</b> to provide 26 iteration functions
       on <b>Backbone.Collection</b>. They aren't all documented here, but
       you can take a look at the Underscore documentation for the full details&hellip;
     </p>
@@ -1135,6 +1135,7 @@ alert(JSON.stringify(collection));
       <li><a href="http://documentcloud.github.com/underscore/#max">max</a></li>
       <li><a href="http://documentcloud.github.com/underscore/#min">min</a></li>
       <li><a href="http://documentcloud.github.com/underscore/#sortBy">sortBy</a></li>
+      <li><a href="http://documentcloud.github.com/underscore/#groupBy">groupBy</a></li>
       <li><a href="http://documentcloud.github.com/underscore/#sortedIndex">sortedIndex</a></li>
       <li><a href="http://documentcloud.github.com/underscore/#toArray">toArray</a></li>
       <li><a href="http://documentcloud.github.com/underscore/#size">size</a></li>