diff --git a/README.md b/README.md
index 9f1bb23c..2fbc5889 100644
--- a/README.md
+++ b/README.md
@@ -189,6 +189,20 @@ If the environment variable is not an integer, you'd get an Exception:
 One or more environment variables failed assertions: FOO is not an integer
 ```
 
+### Boolean Variables
+
+You may need to ensure a variable is in the form of a boolean, accepting "On", "1", "Yes", "Off", "0" and "No". You may do the following:
+
+```php
+$dotenv->required('FOO')->isBoolean();
+```
+
+If the environment variable is not a boolean, you'd get an Exception:
+
+```
+One or more environment variables failed assertions: FOO is not a boolean
+```
+
 ### Allowed Values
 
 It is also possible to define a set of values that your environment variable
diff --git a/src/Validator.php b/src/Validator.php
index aa3cb0e4..53a7fd5a 100644
--- a/src/Validator.php
+++ b/src/Validator.php
@@ -77,6 +77,25 @@ function ($value) {
         );
     }
 
+    /**
+     * Assert that each specified variable is a boolean.
+     *
+     * @return \Dotenv\Validator
+     */
+    public function isBoolean()
+    {
+        return $this->assertCallback(
+            function ($value) {
+                if ($value === '') {
+                    return false;
+                }
+
+                return (filter_var($value, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE) !== NULL);
+            },
+            'is not a boolean'
+        );
+    }
+
     /**
      * Assert that each variable is amongst the given choices.
      *
diff --git a/tests/Dotenv/ValidatorBooleanTest.php b/tests/Dotenv/ValidatorBooleanTest.php
new file mode 100644
index 00000000..14bb8ec7
--- /dev/null
+++ b/tests/Dotenv/ValidatorBooleanTest.php
@@ -0,0 +1,95 @@
+<?php
+
+use Dotenv\Dotenv;
+
+class ValidatorBooleanTest extends PHPUnit_Framework_TestCase
+{
+    /**
+     * @var string
+     */
+    private $fixturesFolder;
+
+    public function setUp()
+    {
+        $this->fixturesFolder = dirname(__DIR__).'/fixtures/env';
+    }
+
+    /**
+     * List of valid boolean values in fixtures/env/booleans.env
+     *
+     * @return array
+     */
+    public function validBooleanValuesDataProvider()
+    {
+        return array(
+            array('VALID_EXPLICIT_LOWERCASE_TRUE'),
+            array('VALID_EXPLICIT_LOWERCASE_FALSE'),
+            array('VALID_EXPLICIT_UPPERCASE_TRUE'),
+            array('VALID_EXPLICIT_UPPERCASE_FALSE'),
+            array('VALID_EXPLICIT_MIXEDCASE_TRUE'),
+            array('VALID_EXPLICIT_MIXEDCASE_FALSE'),
+
+            array('VALID_NUMBER_TRUE'),
+            array('VALID_NUMBER_FALSE'),
+
+            array('VALID_ONOFF_LOWERCASE_TRUE'),
+            array('VALID_ONOFF_LOWERCASE_FALSE'),
+            array('VALID_ONOFF_UPPERCASE_TRUE'),
+            array('VALID_ONOFF_UPPERCASE_FALSE'),
+            array('VALID_ONOFF_MIXEDCASE_TRUE'),
+            array('VALID_ONOFF_MIXEDCASE_FALSE'),
+
+            array('VALID_YESNO_LOWERCASE_TRUE'),
+            array('VALID_YESNO_LOWERCASE_FALSE'),
+            array('VALID_YESNO_UPPERCASE_TRUE'),
+            array('VALID_YESNO_UPPERCASE_FALSE'),
+            array('VALID_YESNO_MIXEDCASE_TRUE'),
+            array('VALID_YESNO_MIXEDCASE_FALSE'),
+        );
+    }
+
+    /**
+     * @dataProvider validBooleanValuesDataProvider
+     */
+    public function testCanValidateBooleans($boolean)
+    {
+        $dotenv = new Dotenv($this->fixturesFolder, 'booleans.env');
+        $dotenv->load();
+
+        $dotenv->required($boolean)->isBoolean();
+
+        $this->assertTrue(true); // anything wrong - an exception will be thrown
+    }
+
+    /**
+     * List of non-boolean values in fixtures/env/booleans.env
+     *
+     * @return array
+     */
+    public function invalidBooleanValuesDataProvider()
+    {
+        return array(
+            array('INVALID_SOMETHING'),
+            array('INVALID_EMPTY'),
+            array('INVALID_EMPTY_STRING'),
+            array('INVALID_NULL'),
+            array('INVALID_NUMBER_POSITIVE'),
+            array('INVALID_NUMBER_NEGATIVE'),
+            array('INVALID_MINUS'),
+            array('INVALID_TILDA'),
+            array('INVALID_EXCLAMATION'),
+        );
+    }
+
+    /**
+     * @dataProvider invalidBooleanValuesDataProvider
+     * @expectedException Dotenv\Exception\ValidationException
+     */
+    public function testCanInvalidateNonBooleans($boolean)
+    {
+        $dotenv = new Dotenv($this->fixturesFolder, 'booleans.env');
+        $dotenv->load();
+
+        $dotenv->required($boolean)->isBoolean();
+    }
+}
diff --git a/tests/fixtures/env/booleans.env b/tests/fixtures/env/booleans.env
new file mode 100644
index 00000000..522ac456
--- /dev/null
+++ b/tests/fixtures/env/booleans.env
@@ -0,0 +1,33 @@
+VALID_EXPLICIT_LOWERCASE_TRUE=true
+VALID_EXPLICIT_LOWERCASE_FALSE=false
+VALID_EXPLICIT_UPPERCASE_TRUE=TRUE
+VALID_EXPLICIT_UPPERCASE_FALSE=FALSE
+VALID_EXPLICIT_MIXEDCASE_TRUE=True
+VALID_EXPLICIT_MIXEDCASE_FALSE=False
+
+VALID_NUMBER_TRUE=1
+VALID_NUMBER_FALSE=0
+
+VALID_ONOFF_LOWERCASE_TRUE=on
+VALID_ONOFF_LOWERCASE_FALSE=off
+VALID_ONOFF_UPPERCASE_TRUE=ON
+VALID_ONOFF_UPPERCASE_FALSE=OFF
+VALID_ONOFF_MIXEDCASE_TRUE=On
+VALID_ONOFF_MIXEDCASE_FALSE=Off
+
+VALID_YESNO_LOWERCASE_TRUE=yes
+VALID_YESNO_LOWERCASE_FALSE=no
+VALID_YESNO_UPPERCASE_TRUE=YES
+VALID_YESNO_UPPERCASE_FALSE=NO
+VALID_YESNO_MIXEDCASE_TRUE=Yes
+VALID_YESNO_MIXEDCASE_FALSE=No
+
+INVALID_SOMETHING=something
+INVALID_EMPTY=
+INVALID_EMPTY_STRING=""
+INVALID_NULL=null
+INVALID_NUMBER_POSITIVE=2
+INVALID_NUMBER_NEGATIVE=-2
+INVALID_MINUS=-
+INVALID_TILDA=~
+INVALID_EXCLAMATION=!