Index: src/js/_enqueues/admin/widgets.js
===================================================================
--- src/js/_enqueues/admin/widgets.js	(revision 45536)
+++ src/js/_enqueues/admin/widgets.js	(working copy)
@@ -501,6 +501,44 @@
 				self.closeChooser();
 			}
 		});
+
+		/**
+		 * Use feature detection to determine whether inputs should use
+		 * the `keyup` or `input` event. Input is preferred but lacks support
+		 * in legacy browsers. See changeset 34078, see also ticket #26600#comment:59
+		 */
+		if ( 'oninput' in document.createElement( 'input' ) ) {
+			inputEvent = 'input';
+		} else {
+			inputEvent = 'keyup';
+		}
+
+		$( '#widgets-search-input' ).on( inputEvent, function() {
+
+			var search_term   = $('#widgets-search-input').val() || '',
+				parent        = $('#widgets-left'),
+				widgets       = parent.find('.widget'),
+				widget_titles = parent.find('.widget-title');
+
+			if( search_term.length ) {
+
+				// Hide all widgets. Because, Below we show those widgets
+				// which have search term in the widget title.
+				widgets.addClass('hide-widget').removeClass('show-widget');
+
+				// Search widget and ONLY show these widgets which "contain" the widget title.
+				var rex = new RegExp( search_term, 'i');
+		        widget_titles.filter(function () {
+					var widget_name = $.trim( $(this).text() ) || '';
+		        	return rex.test( widget_name );
+		        }).parents('.widget').removeClass('hide-widget').addClass('show-widget');
+
+			} else {
+
+				// Show all widgets.
+				widgets.removeClass('hide-widget').addClass('show-widget');
+			}
+		});
 	},
 
 	saveOrder : function( sidebarId ) {
Index: src/wp-admin/css/widgets.css
===================================================================
--- src/wp-admin/css/widgets.css	(revision 45536)
+++ src/wp-admin/css/widgets.css	(working copy)
@@ -773,6 +773,28 @@
 	cursor: not-allowed;
 }
 
+/* =Widget Search
+-------------------------------------------------------------- */
+#widgets-search-input {
+	margin: 0 0 .2em 0;
+	width: 100%;
+	font-size: 16px;
+	font-weight: 300;
+	line-height: 1.5;
+	border-width: 1px;
+	border-style: solid;
+	border-color: #ddd;
+}
+
+
+.show-widget {
+    display: block;
+}
+
+.hide-widget {
+    display: none;
+}
+
 /* =Media Queries
 -------------------------------------------------------------- */
 
Index: src/wp-admin/widgets.php
===================================================================
--- src/wp-admin/widgets.php	(revision 45536)
+++ src/wp-admin/widgets.php	(working copy)
@@ -426,6 +426,9 @@
 
 <div class="widget-liquid-left">
 <div id="widgets-left">
+	<div class="widgets-search">
+		<input type="search" id="widgets-search-input" class="regular-text" placeholder="<?php _e('Search widgets...'); ?>">
+	</div>
 	<div id="available-widgets" class="widgets-holder-wrap">
 		<div class="sidebar-name">
 			<button type="button" class="handlediv hide-if-no-js" aria-expanded="true">