Index: wp-includes/class-wp-theme.php
===================================================================
--- wp-includes/class-wp-theme.php	(revision 26862)
+++ wp-includes/class-wp-theme.php	(working copy)
@@ -904,6 +904,47 @@
 	}
 
 	/**
+	 * Returns an array with all the theme's screenshots, checking for files
+	 * in the form of 'screenshot-n' at the root of a theme directory.
+	 *
+	 * Maximum allowed is five screenshots total.
+	 *
+	 * @todo Hardcoded to pngs -- support jpg, etc.
+	 * @todo Set up caching.
+	 *
+	 * @see WP_Theme::get_screenshot()
+	 *
+	 * @param a theme object
+	 * @return array Screenshots. First element is default screenshot.
+	 */
+	public function get_multiple_screenshots() {
+		$base = $this->get_stylesheet_directory_uri();
+		$set = array( 2, 3, 4, 5 );
+
+		// Return early if there is no main screenshot
+		if ( $this->get_screenshot() ) {
+			return false;
+		}
+
+		// Screenshots array starts with default screenshot at position [0]
+		$screenshots = array( $this->get_screenshot() );
+
+		// Check how many other screenshots a theme has
+		foreach ( $set as $number ) {
+			// Hard-coding file path for pngs...
+			$file = '/screenshot-' . $number . '.png';
+			$path = $this->template_dir . $file;
+
+			if ( ! file_exists( $path ) )
+				continue;
+
+			$screenshots[] = $base . $file;
+		}
+
+		return $screenshots;
+	}
+
+	/**
 	 * Return files in the theme's directory.
 	 *
 	 * @since 3.4.0
Index: wp-admin/includes/theme.php
===================================================================
--- wp-admin/includes/theme.php	(revision 26862)
+++ wp-admin/includes/theme.php	(working copy)
@@ -411,7 +411,7 @@
 		$prepared_themes[ $slug ] = array(
 			'id'           => $slug,
 			'name'         => $theme->display( 'Name' ),
-			'screenshot'   => array( $theme->get_screenshot() ), // @todo multiple
+			'screenshot'   => $theme->get_multiple_screenshots(),
 			'description'  => $theme->display( 'Description' ),
 			'author'       => $theme->display( 'Author', false, true ),
 			'authorAndUri' => $theme->display( 'Author' ),
Index: wp-admin/js/theme.js
===================================================================
--- wp-admin/js/theme.js	(revision 26862)
+++ wp-admin/js/theme.js	(working copy)
@@ -363,6 +363,28 @@
 		if ( image.width && image.width <= 300 ) {
 			el.addClass( 'small-screenshot' );
 		}
+	},
+
+	// Setups an image gallery using the theme screenshots supplied by a theme
+	screenshotGallery: function() {
+		var el, img,
+			screenshots = $( '.theme-screenshots' );
+
+		// Select the first item
+		screenshots.find( '.thumb' ).first().addClass( 'selected' );
+
+		// Clicking on a screenshot thumbnail drops it
+		// at the top of the stack in a larger size
+		screenshots.on( 'click', 'div.thumb', function() {
+			el = $( this );
+			img = $( this ).find( 'img' ).attr( 'src' );
+
+			// Change src attribute of first image
+			screenshots.find( '.screenshot' ).first().find( 'img' ).attr( 'src', img );
+			// Mark the new image as 'selected'
+			el.siblings( '.selected' ).removeClass( 'selected' );
+			el.addClass( 'selected' );
+		});
 	}
 });
 
@@ -538,6 +560,7 @@
 
 		this.overlay.render();
 		this.$overlay.html( this.overlay.el );
+		this.overlay.screenshotGallery();
 
 		// Bind to theme:next and theme:previous
 		// triggered by the arrow keys
Index: wp-admin/css/wp-admin.css
===================================================================
--- wp-admin/css/wp-admin.css	(revision 26862)
+++ wp-admin/css/wp-admin.css	(working copy)
@@ -6877,7 +6877,6 @@
 	margin: 0 30px 0 0;
 	width: 55%;
 	max-width: 880px;
-	text-align: center;
 }
 
 /* First screenshot, shown big */
@@ -6918,13 +6917,13 @@
 /* Other screenshots, shown small and square */
 .theme-overlay .screenshot.thumb {
 	background: #ccc;
-	border: 1px solid #eee;
+	border: 2px solid #fff;
 	float: none;
 	display: inline-block;
-	margin: 10px 5px 0;
-	width: 140px;
-	height: 80px;
+	margin: 10px 5px 0 0;
+	width: 80px;
 	cursor: pointer;
+	padding: 3px;
 }
 
 .theme-overlay .screenshot.thumb:after {
@@ -6935,21 +6934,22 @@
 
 .theme-overlay .screenshot.thumb img {
 	cursor: pointer;
+	width: 300px;
 	height: auto;
 	position: absolute;
-	left: 0;
-	top: 0;
-	width: 100%;
-	height: auto;
+		left: 0;
+		top: 0;
+	box-sizing: border-box;
 }
 
 .theme-overlay .screenshot.selected {
-	background: transparent;
-	border: 2px solid #2ea2cc;
+	background: #0074a2;
+	border-color: #0074a2;
+	box-shadow: none;
 }
 
 .theme-overlay .screenshot.selected img {
-	opacity: 0.8;
+	opacity: 0.6;
 }
 
 /* No screenshot placeholder */
Index: wp-admin/themes.php
===================================================================
--- wp-admin/themes.php	(revision 26862)
+++ wp-admin/themes.php	(working copy)
@@ -317,6 +317,15 @@
 			<div class="theme-screenshots">
 			<# if ( data.screenshot[0] ) { #>
 				<div class="screenshot"><img src="{{ data.screenshot[0] }}" alt="" /></div>
+				<#
+					if ( _.size( data.screenshot ) > 1 ) {
+						_.each ( data.screenshot, function( image ) {
+				#>
+					<div class="screenshot thumb"><img src="{{ image }}" alt="" /></div>
+				<#
+						});
+					}
+				#>
 			<# } else { #>
 				<div class="screenshot blank"></div>
 			<# } #>