diff --git a/index.html b/index.html
index eacb7016e..2eb2dbc31 100644
--- a/index.html
+++ b/index.html
@@ -813,6 +813,18 @@ _.isElement(jQuery('body')[0]);
 => false
 _.isArray([1,2,3]);
 => true
+</pre>
+
+      <p id="isArguments">
+        <b class="header">isArguments</b><code>_.isArguments(object)</code>
+        <br />
+        Returns <i>true</i> if <b>object</b> is an Arguments object.
+      </p>
+      <pre>
+(function(){ return _.isArguments(arguments); })(1, 2, 3);
+=&gt; true
+_.isArguments([1,2,3]);
+=&gt; false
 </pre>
 
       <p id="isFunction">
diff --git a/test/collections.js b/test/collections.js
index 47ca9d430..935edcb95 100644
--- a/test/collections.js
+++ b/test/collections.js
@@ -29,6 +29,10 @@ $(document).ready(function() {
     answer = null;
     _.each([1, 2, 3], function(num, index, arr){ if (_.include(arr, num)) answer = true; });
     ok(answer, 'can reference the original collection from inside the iterator');
+
+    answers = [];
+    _.each({range : 1, speed : 2, length : 3}, function(v){ answers.push(v); });
+    ok(answers.join(', '), '1, 2, 3', 'can iterate over objects with numeric length properties');
   });
 
   test('collections: map', function() {
diff --git a/test/objects.js b/test/objects.js
index 8ba67858e..cd45c0bc6 100644
--- a/test/objects.js
+++ b/test/objects.js
@@ -14,7 +14,7 @@ $(document).ready(function() {
     var expected = ["all", "any", "bind", "bindAll", "breakLoop", "clone", "compact",
     "compose","defer", "delay", "detect", "each", "every", "extend", "filter", "first",
     "flatten", "foldl", "foldr", "forEach", "functions", "head", "identity", "include",
-    "indexOf", "inject", "intersect", "invoke", "isArray", "isDate", "isElement", "isEmpty", "isEqual",
+    "indexOf", "inject", "intersect", "invoke", "isArguments", "isArray", "isDate", "isElement", "isEmpty", "isEqual",
     "isFunction", "isNaN", "isNull", "isNumber", "isRegExp", "isString", "isUndefined", "keys", "last", "lastIndexOf", "map", "max",
     "methods", "min", "noConflict", "pluck", "range", "reduce", "reduceRight", "reject", "rest", "select",
     "size", "some", "sortBy", "sortedIndex", "tail", "template", "toArray", "uniq",
@@ -71,6 +71,13 @@ $(document).ready(function() {
     ok(_.isElement($('html')[0]), 'the html tag is a DOM element');
   });
 
+  test("objects: isArguments", function() {
+    var args = (function(){ return arguments; })(1, 2, 3);
+    ok(_.isArguments(args), 'the arguments object is an arguments object');
+    ok(!_.isArguments(_.toArray(args)), 'but not when it\'s converted into an array');
+    ok(!_.isArguments([1,2,3]), 'and not vanilla arrays.');
+  });
+
   test("objects: isArray", function() {
     ok(!_.isArray(arguments), 'the arguments object is not an array');
     ok(_.isArray([1, 2, 3]), 'but arrays are');
diff --git a/underscore.js b/underscore.js
index 7ae664386..810531f72 100644
--- a/underscore.js
+++ b/underscore.js
@@ -30,8 +30,12 @@
   // Export the Underscore object for CommonJS.
   if (typeof exports !== 'undefined') exports._ = _;
 
-  // Create quick reference variables for speed access to Object.prototype.
-  var toString = Object.prototype.toString, hasOwnProperty = Object.prototype.hasOwnProperty;
+  // Create quick reference variables for speed access to core prototypes.
+  var slice                 = Array.prototype.slice,
+      unshift               = Array.prototype.unshift,
+      toString              = Object.prototype.toString,
+      hasOwnProperty        = Object.prototype.hasOwnProperty,
+      propertyIsEnumerable  = Object.prototype.propertyIsEnumerable;
 
   // Current version.
   _.VERSION = '0.5.0';
@@ -45,7 +49,7 @@
     try {
       if (obj.forEach) {
         obj.forEach(iterator, context);
-      } else if (_.isNumber(obj.length)) {
+      } else if (_.isArray(obj) || _.isArguments(obj)) {
         for (var i=0, l=obj.length; i<l; i++) iterator.call(context, obj[i], i, obj);
       } else {
         var keys = _.keys(obj), l = keys.length;
@@ -218,9 +222,10 @@
 
   // Convert anything iterable into a real, live array.
   _.toArray = function(iterable) {
-    if (!iterable)           return [];
-    if (iterable.toArray)    return iterable.toArray();
-    if (_.isArray(iterable)) return iterable;
+    if (!iterable)                return [];
+    if (iterable.toArray)         return iterable.toArray();
+    if (_.isArray(iterable))      return iterable;
+    if (_.isArguments(iterable))  return slice.call(iterable);
     return _.map(iterable, function(val){ return val; });
   };
 
@@ -235,7 +240,7 @@
   // values in the array. Aliased as "head". The "guard" check allows it to work
   // with _.map.
   _.first = function(array, n, guard) {
-    return n && !guard ? Array.prototype.slice.call(array, 0, n) : array[0];
+    return n && !guard ? slice.call(array, 0, n) : array[0];
   };
 
   // Returns everything but the first entry of the array. Aliased as "tail".
@@ -243,7 +248,7 @@
   // the rest of the values in the array from that index onward. The "guard"
    //check allows it to work with _.map.
   _.rest = function(array, index, guard) {
-    return Array.prototype.slice.call(array, _.isUndefined(index) || guard ? 1 : index);
+    return slice.call(array, _.isUndefined(index) || guard ? 1 : index);
   };
 
   // Get the last element of an array.
@@ -406,6 +411,11 @@
     return _.map(obj, _.identity);
   };
 
+  // Return a sorted list of the function names available in Underscore.
+  _.functions = function(obj) {
+    return _.select(_.keys(obj), function(key){ return _.isFunction(obj[key]); }).sort();
+  };
+
   // Extend a given object with all of the properties in a source object.
   _.extend = function(destination, source) {
     for (var property in source) destination[property] = source[property];
@@ -464,6 +474,11 @@
     return !!(obj && obj.nodeType == 1);
   };
 
+  // Is a given variable an arguments object?
+  _.isArguments = function(obj) {
+    return obj && _.isNumber(obj.length) && !_.isArray(obj) && !propertyIsEnumerable.call(obj, 'length');
+  };
+
   // Is the given value NaN -- this one is interesting. NaN != NaN, and
   // isNaN(undefined) == true, so we make sure it's a number first.
   _.isNaN = function(obj) {
@@ -522,11 +537,6 @@
     return prefix ? prefix + id : id;
   };
 
-  // Return a sorted list of the function names available in Underscore.
-  _.functions = function(obj) {
-    return _.select(_.keys(obj), function(key){ return _.isFunction(obj[key]); }).sort();
-  };
-
   // JavaScript templating a-la ERB, pilfered from John Resig's
   // "Secrets of the JavaScript Ninja", page 83.
   _.template = function(str, data) {
@@ -566,7 +576,7 @@
 
   // Add all of the Underscore functions to the wrapper object.
   _.each(_.functions(_), function(name) {
-    var method = _[name], unshift = Array.prototype.unshift;
+    var method = _[name];
     wrapper.prototype[name] = function() {
       unshift.call(arguments, this._wrapped);
       return result(method.apply(_, arguments), this._chain);