diff --git a/README.md b/README.md
index 9382df2..c2f7195 100644
--- a/README.md
+++ b/README.md
@@ -133,6 +133,7 @@ V::lang('ar');
  * `contains` - Field is a string and contains the given string
  * `creditCard` - Field is a valid credit card number
  * `instanceOf` - Field contains an instance of the given class
+ * `optional` - Value does not need to be included in data array. If it is however, it must pass validation.
 
 **NOTE**: If you are comparing floating-point numbers with min/max validators, you
 should install the [BCMath](http://us3.php.net/manual/en/book.bc.php)