diff --git a/src/core.js b/src/core.js
index 74d195e42..93fe25568 100644
--- a/src/core.js
+++ b/src/core.js
@@ -375,7 +375,8 @@ $.extend( $.validator, {
 			this.invalid = {};
 			this.reset();
 
-			var groups = ( this.groups = {} ),
+			var currentForm = this.currentForm,
+				groups = ( this.groups = {} ),
 				rules;
 			$.each( this.settings.groups, function( key, value ) {
 				if ( typeof value === "string" ) {
@@ -398,6 +399,12 @@ $.extend( $.validator, {
 					this.name = $( this ).attr( "name" );
 				}
 
+				// Ignore the element if it belongs to another form. This will happen mainly
+				// when setting the `form` attribute of an input to the id of another form.
+				if ( currentForm !== this.form ) {
+					return;
+				}
+
 				var validator = $.data( this.form, "validator" ),
 					eventType = "on" + event.type.replace( /^validate/, "" ),
 					settings = validator.settings;
@@ -631,6 +638,11 @@ $.extend( $.validator, {
 					this.name = name;
 				}
 
+				// Ignore elements that belong to other/nested forms
+				if ( this.form !== validator.currentForm ) {
+					return false;
+				}
+
 				// Select only the first element for each name, and only those with rules specified
 				if ( name in rulesCache || !validator.objectLength( $( this ).rules() ) ) {
 					return false;
diff --git a/test/index.html b/test/index.html
index 3235689da..0079aa7d9 100644
--- a/test/index.html
+++ b/test/index.html
@@ -113,7 +113,7 @@ <h2 id="qunit-userAgent"></h2>
 		<input data-rule-greaterThan="#y1" value="10" name="y2" id="y2">
 		<input data-rule-lessThanEqual="#z2" value="10" name="z1" id="z1">
 		<input data-rule-greaterThanEqual="#z1" value="10" name="z2" id="z2">
-	</form> 
+	</form>
 	<form id="testForm6">
 		<input data-rule-required="true" data-rule-minlength="2" type="checkbox" name="check" id="form6check1">
 		<input type="checkbox" name="check" id="form6check2">
@@ -449,6 +449,9 @@ <h3></h3>
 		<br>
 		<input type="text" name="something" id="_something" />
 	</form>
+	<form id="testForm28">
+		<input type="text" name="f28input" required>
+	</form>
 </div>
 </body>
 </html>
diff --git a/test/test.js b/test/test.js
index 79bf0cf1b..dbe901556 100644
--- a/test/test.js
+++ b/test/test.js
@@ -187,6 +187,173 @@ QUnit.test( "valid(), ignores ignored elements", function( assert ) {
 	assert.ok( $( "#firstnamec" ).valid() );
 } );
 
+QUnit.test( "valid() should ignore elements that belong to other/nested forms", function( assert ) {
+	var form = $( "#testForm28" );
+
+	form.validate();
+
+	// 1. Test with nested form
+	form.append(
+		"<form id='testForm28-nested'>" +
+		"    <input type='text' name='f28nestedinput' required>" +
+		"</form>"
+	);
+
+	try {
+		form.valid();
+		assert.ok( true, "It should ignore the input of nested form" );
+	} catch ( err ) {
+		assert.ok( false, "Shouldn't throw an error" );
+	}
+
+	// Remove the validator atteched to testForm28
+	form.removeData( "validator" );
+	$( "#testForm28-nested" ).remove();
+
+	// 2. Test using another form outside of validated one
+	form.parent().append(
+		"<form id='testForm28-other'>" +
+		"   <input type='text' name='f28otherinput' required>" +
+		"   <input type='text' name='f28input' form='testForm28' required>" +
+		"</form>"
+	);
+
+	$( "#testForm28-other" ).validate();
+
+	try {
+		$( "#testForm28-other" ).valid();
+		assert.ok( true, "It should ignore the input of other form" );
+	} catch ( err ) {
+		assert.ok( false, "Shouldn't throw an error" );
+	}
+
+	$( "#testForm28-other" ).remove();
+} );
+
+QUnit.test( "form() should ignore elements that belong to other/nested forms", function( assert ) {
+	var form = $( "#testForm28" );
+	var v = form.validate();
+
+	form.validate();
+
+	// 1. Test with nested form
+	form.append(
+		"<form id='testForm28-nested'>" +
+		"    <input type='text' name='f28nestedinput' required>" +
+		"</form>"
+	);
+
+	try {
+		v.form();
+		assert.ok( true, "It should ignore the input of nested form" );
+	} catch ( err ) {
+		assert.ok( false, "Shouldn't throw an error" );
+	}
+
+	// Remove the validator atteched to testForm28
+	form.removeData( "validator" );
+	$( "#testForm28-nested" ).remove();
+
+	// 2. Test using another form outside of validated one
+	form.parent().append(
+		"<form id='testForm28-other'>" +
+		"   <input type='text' name='f28otherinput' required>" +
+		"   <input type='text' name='f28input' form='testForm28' required>" +
+		"</form>"
+	);
+
+	v = $( "#testForm28-other" ).validate();
+
+	try {
+		v.form();
+		assert.ok( true, "It should ignore the input of other form" );
+	} catch ( err ) {
+		assert.ok( false, "Shouldn't throw an error" );
+	}
+
+	$( "#testForm28-other" ).remove();
+} );
+
+QUnit.test( "elements() should ignore elements that belong to other/nested forms", function( assert ) {
+	var form = $( "#testForm28" );
+	var v = form.validate();
+
+	// 1. Test with nested form
+	form.append(
+		"<form id='testForm28-nested'>" +
+		"    <input type='text' name='f28nestedinput' required>" +
+		"</form>"
+	);
+
+	try {
+		assert.equal( v.elements().length, 1, "There should be only one element to validate" );
+	} catch ( err ) {
+		assert.ok( false, "Shouldn't throw an error" );
+	}
+
+	// Remove the validator atteched to testForm28
+	form.removeData( "validator" );
+	$( "#testForm28-nested" ).remove();
+
+	// 2. Test using another form outside of validated one
+	form.parent().append(
+		"<form id='testForm28-other'>" +
+		"   <input type='text' name='f28otherinput' required>" +
+		"   <input type='text' name='f28input' form='testForm28' required>" +
+		"</form>"
+	);
+
+	v = $( "#testForm28-other" ).validate();
+
+	try {
+		assert.equal( v.elements().length, 1, "There should be only one element to validate" );
+	} catch ( err ) {
+		assert.ok( false, "Shouldn't throw an error" );
+	}
+
+	$( "#testForm28-other" ).remove();
+} );
+
+QUnit.test( "Ignore elements that have form attribute set to other forms", function( assert ) {
+
+	// Append a form that contains an input with form attribute set to "testForm28"
+	$( "#testForm28" ).parent().append(
+		"<form id='testForm28-other'>" +
+		"   <input type='text' name='f28otherinput' required>" +
+		"   <input type='text' name='f28input' form='testForm28' required>" +
+		"</form>"
+	);
+
+	// Attach the plugin to the appended form
+	$( "#testForm28-other" ).validate();
+
+	// 1. Simulate typing
+	try {
+		$( "[name='f28input']", "#testForm28-other" ).trigger( "keyup" );
+		assert.ok( true, "It should ignore the input of other form" );
+	} catch ( err ) {
+		assert.ok( false, "Shouldn't throw an error while typing" );
+	}
+
+	// 2. Simulate forcussing in the input
+	try {
+		$( "[name='f28input']", "#testForm28-other" ).trigger( "focusin" );
+		assert.ok( true, "It should ignore the input of other form" );
+	} catch ( err ) {
+		assert.ok( false, "Shouldn't throw an error on focus" );
+	}
+
+	// 3. Simulate focussing out the input
+	try {
+		$( "[name='f28input']", "#testForm28-other" ).trigger( "focusout" );
+		assert.ok( true, "It should ignore the input of other form" );
+	} catch ( err ) {
+		assert.ok( false, "Shouldn't throw an error on blur" );
+	}
+
+	$( "#testForm28-other" ).remove();
+} );
+
 QUnit.test( "addMethod", function( assert ) {
 	assert.expect( 3 );
 	$.validator.addMethod( "hi", function( value ) {