diff --git src/wp-includes/class.wp-scripts.php src/wp-includes/class.wp-scripts.php
index fbb8b22..a831ff9 100644
--- src/wp-includes/class.wp-scripts.php
+++ src/wp-includes/class.wp-scripts.php
@@ -95,15 +95,24 @@ class WP_Scripts extends WP_Dependencies {
 		if ( false === $group && in_array($handle, $this->in_footer, true) )
 			$this->in_footer = array_diff( $this->in_footer, (array) $handle );
 
-		if ( null === $this->registered[$handle]->ver )
+		$obj = $this->registered[$handle];
+
+		if ( null === $obj->ver )
 			$ver = '';
 		else
-			$ver = $this->registered[$handle]->ver ? $this->registered[$handle]->ver : $this->default_version;
+			$ver = $obj->ver ? $obj->ver : $this->default_version;
 
 		if ( isset($this->args[$handle]) )
 			$ver = $ver ? $ver . '&' . $this->args[$handle] : $this->args[$handle];
 
-		$src = $this->registered[$handle]->src;
+		$src = $obj->src;
+		$cond_before = $cond_after = '';
+		$conditional = isset( $obj->extra['conditional'] ) ? $obj->extra['conditional'] : '';
+
+		if ( $conditional ) {
+			$cond_before = "<!--[if {$conditional}]>\n";
+			$cond_after = "\n<![endif]-->";
+		}
 
 		if ( $this->do_concat ) {
 			/**
@@ -115,7 +124,7 @@ class WP_Scripts extends WP_Dependencies {
 			 * @param string $handle Script handle.
 			 */
 			$srce = apply_filters( 'script_loader_src', $src, $handle );
-			if ( $this->in_default_dir($srce) ) {
+			if ( $this->in_default_dir( $srce ) && ! $conditional ) {
 				$this->print_code .= $this->print_extra_script( $handle, false );
 				$this->concat .= "$handle,";
 				$this->concat_version .= "$handle$ver";
@@ -140,7 +149,7 @@ class WP_Scripts extends WP_Dependencies {
 		if ( ! $src )
 			return true;
 
-		$tag = "<script type='text/javascript' src='$src'></script>\n";
+		$tag = "{$cond_before}<script type='text/javascript' src='$src'></script>{$cond_after}\n";
 
 		/** 
 		 * Filter the HTML script tag of an enqueued script.
diff --git src/wp-includes/functions.wp-scripts.php src/wp-includes/functions.wp-scripts.php
index 6eb7a44..1a77df8 100644
--- src/wp-includes/functions.wp-scripts.php
+++ src/wp-includes/functions.wp-scripts.php
@@ -258,3 +258,26 @@ function wp_script_is( $handle, $list = 'enqueued' ) {
 
 	return (bool) $wp_scripts->query( $handle, $list );
 }
+
+
+/**
+ * Add metadata to a script.
+ *
+ * Works only if the script has already been added.
+ *
+ * Possible values for $key and $value:
+ * 'conditional' string Comments for IE 6, lte IE 7, etc.
+ *
+ * @see WP_Dependency::add_data()
+ *
+ * @since 4.2.0
+ *
+ * @param string $handle Name of the script.
+ * @param string $key    Name of data point for which we're storing a value.
+ * @param mixed  $value  String containing the data to be added.
+ * @return bool True on success, false on failure.
+ */
+function wp_script_add_data( $handle, $key, $value ){
+	global $wp_scripts;
+	return $wp_scripts->add_data( $handle, $key, $value );
+}
diff --git tests/phpunit/tests/dependencies/scripts.php tests/phpunit/tests/dependencies/scripts.php
index 3f4e724..783cf00 100644
--- tests/phpunit/tests/dependencies/scripts.php
+++ tests/phpunit/tests/dependencies/scripts.php
@@ -84,4 +84,21 @@ class Tests_Dependencies_Scripts extends WP_UnitTestCase {
 		// Cleanup
 		$wp_scripts->base_url = $base_url_backup;
 	}
+
+	/**
+	 * Test Conditional Comments
+	 * @ticket 10624
+	 */
+	function test_wp_script_add_data() {
+		// Enqueue & add conditional comments
+		wp_enqueue_script( 'twentytwelve-html5', 'example.com', array(), '1.0' );
+		wp_script_add_data( 'twentytwelve-html5', 'conditional', 'lt IE 9' );
+		$expected = "<!--[if lt IE 9]>\n<script type='text/javascript' src='http://example.com?ver=1.0'></script>\n<![endif]-->\n";
+
+		// Go!
+		$this->assertEquals( $expected, get_echo( 'wp_print_scripts' ) );
+
+		// No scripts left to print
+		$this->assertEquals( '', get_echo( 'wp_print_scripts' ) );
+	}
 }