diff --git a/activesupport/CHANGELOG b/activesupport/CHANGELOG
index 4edeadf10c0d7..cc4a2ff90ecee 100644
--- a/activesupport/CHANGELOG
+++ b/activesupport/CHANGELOG
@@ -1,5 +1,7 @@
 *Edge*
 
+* Add Enumerable#exclude? to bring parity to Enumerable#include? and avoid if !x.include?/else calls [DHH]
+
 * Update Edinburgh TimeZone to use "Europe/London" instead of "Europe/Dublin" #3310 [Phil Ross]
 
 * Update bundled TZInfo to v0.3.15 [Geoff Buesing]
diff --git a/activesupport/lib/active_support/core_ext/enumerable.rb b/activesupport/lib/active_support/core_ext/enumerable.rb
index b11c916f61930..d0821a7c68177 100644
--- a/activesupport/lib/active_support/core_ext/enumerable.rb
+++ b/activesupport/lib/active_support/core_ext/enumerable.rb
@@ -101,6 +101,11 @@ def many?(&block)
     size = block_given? ? select(&block).size : self.size
     size > 1
   end
+  
+  # The negative of the Enumerable#include?. Returns true if the collection does not include the object.
+  def exclude?(object)
+    !include?(object)
+  end
 end
 
 class Range #:nodoc:
diff --git a/activesupport/test/core_ext/enumerable_test.rb b/activesupport/test/core_ext/enumerable_test.rb
index 66f5f9fbdec5a..4650b796b626b 100644
--- a/activesupport/test/core_ext/enumerable_test.rb
+++ b/activesupport/test/core_ext/enumerable_test.rb
@@ -89,4 +89,9 @@ def test_many
     assert ![ 1, 2 ].many? {|x| x > 1 }
     assert [ 1, 2, 2 ].many? {|x| x > 1 }
   end
+  
+  def test_exclude?
+    assert [ 1 ].exclude?(2)
+    assert ![ 1 ].exclude?(1)
+  end
 end