diff --git a/src/wp-admin/css/common.css b/src/wp-admin/css/common.css
index 7f3c1a1f00..2ec8b7d22a 100644
--- a/src/wp-admin/css/common.css
+++ b/src/wp-admin/css/common.css
@@ -215,7 +215,7 @@ body {
 body {
 	background: #f1f1f1;
 	color: #444;
-	font-family: "Open Sans", sans-serif;
+	font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 	font-size: 13px;
 	line-height: 1.4em;
 	min-width: 600px;
diff --git a/src/wp-admin/css/customize-controls.css b/src/wp-admin/css/customize-controls.css
index 82d9801e48..7991e4be6c 100644
--- a/src/wp-admin/css/customize-controls.css
+++ b/src/wp-admin/css/customize-controls.css
@@ -1219,7 +1219,7 @@ body.cheatin h1 {
 	border-bottom: 1px solid #ddd;
 	clear: both;
 	color: #666;
-	font: 24px "Open Sans", sans-serif;
+	font: 24px -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 	margin: 30px 0 0 0;
 	padding: 0;
 	padding-bottom: 7px;
diff --git a/src/wp-admin/css/dashboard.css b/src/wp-admin/css/dashboard.css
index 3968a979f9..4e6d9303ed 100644
--- a/src/wp-admin/css/dashboard.css
+++ b/src/wp-admin/css/dashboard.css
@@ -951,8 +951,6 @@ a.rsswidget {
 	color: #fff;
 }
 
-/* Make the browser nags easier to read with Open Sans */
-
 #dashboard_browser_nag h2.hndle {
 	border: none;
 	font-weight: 600;
diff --git a/src/wp-admin/css/install.css b/src/wp-admin/css/install.css
index 55fbe54330..1524b4a3e3 100644
--- a/src/wp-admin/css/install.css
+++ b/src/wp-admin/css/install.css
@@ -6,7 +6,7 @@ html {
 body {
 	background: #fff;
 	color: #444;
-	font-family: "Open Sans", sans-serif;
+	font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 	margin: 140px auto 25px;
 	padding: 20px 20px 10px 20px;
 	max-width: 700px;
@@ -132,7 +132,7 @@ label {
 }
 textarea {
 	border: 1px solid #ddd;
-	font-family: "Open Sans", sans-serif;
+	font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif
 	width: 100%;
 	-webkit-box-sizing: border-box;
 	-moz-box-sizing: border-box;
@@ -181,7 +181,7 @@ textarea {
 
 input,
 submit {
-	font-family: "Open Sans", sans-serif;
+	font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 }
 
 .form-table input[type=text],
diff --git a/src/wp-admin/css/login.css b/src/wp-admin/css/login.css
index dc77b571fa..d53eabf44e 100644
--- a/src/wp-admin/css/login.css
+++ b/src/wp-admin/css/login.css
@@ -12,7 +12,7 @@ body {
 	background: #f1f1f1;
 	min-width: 0;
 	color: #444;
-	font-family: "Open Sans", sans-serif;
+	font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 	font-size: 13px;
 	line-height: 1.4em;
 }
diff --git a/src/wp-admin/css/press-this-editor.css b/src/wp-admin/css/press-this-editor.css
index 96ff426168..3689c9395e 100644
--- a/src/wp-admin/css/press-this-editor.css
+++ b/src/wp-admin/css/press-this-editor.css
@@ -77,7 +77,7 @@ object {
 */
 body {
 	color: #404040;
-	font-family: "Open Sans", Helvetica, Arial, sans-serif;
+	font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 	font-size: 20px;
 	font-weight: 400;
 	line-height: 1.6;
diff --git a/src/wp-admin/css/press-this.css b/src/wp-admin/css/press-this.css
index 73dadce4e7..ca52b975b1 100644
--- a/src/wp-admin/css/press-this.css
+++ b/src/wp-admin/css/press-this.css
@@ -294,7 +294,7 @@ input,
 select,
 textarea {
 	color: #404040;
-	font-family: "Open Sans", Helvetica, Arial, sans-serif;
+	font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 	font-size: 20px;
 	font-weight: 400;
 	line-height: 1.6;
diff --git a/src/wp-admin/includes/class-wp-press-this.php b/src/wp-admin/includes/class-wp-press-this.php
index 4a909abfbc..bb5ec1b97b 100644
--- a/src/wp-admin/includes/class-wp-press-this.php
+++ b/src/wp-admin/includes/class-wp-press-this.php
@@ -793,36 +793,7 @@ class WP_Press_This {
 			$press_this = str_replace( '.css', '-rtl.css', $press_this );
 		}
 
-		$open_sans_font_url = '';
-
-		/* translators: If there are characters in your language that are not supported
-		 * by Open Sans, translate this to 'off'. Do not translate into your own language.
-		 */
-		if ( 'off' !== _x( 'on', 'Open Sans font: on or off' ) ) {
-			$subsets = 'latin,latin-ext';
-
-			/* translators: To add an additional Open Sans character subset specific to your language,
-			 * translate this to 'greek', 'cyrillic' or 'vietnamese'. Do not translate into your own language.
-			 */
-			$subset = _x( 'no-subset', 'Open Sans font: add new subset (greek, cyrillic, vietnamese)' );
-
-			if ( 'cyrillic' == $subset ) {
-				$subsets .= ',cyrillic,cyrillic-ext';
-			} elseif ( 'greek' == $subset ) {
-				$subsets .= ',greek,greek-ext';
-			} elseif ( 'vietnamese' == $subset ) {
-				$subsets .= ',vietnamese';
-			}
-
-			$query_args = array(
-				'family' => urlencode( 'Open Sans:400italic,700italic,400,600,700' ),
-				'subset' => urlencode( $subsets ),
-			);
-
-			$open_sans_font_url = ',' . add_query_arg( $query_args, 'https://fonts.googleapis.com/css' );
-		}
-
-		return $styles . $press_this . $open_sans_font_url;
+		return $styles . $press_this;
 	}
 
 	/**
diff --git a/src/wp-includes/css/admin-bar.css b/src/wp-includes/css/admin-bar.css
index 9371a94043..c57c1e04e0 100644
--- a/src/wp-includes/css/admin-bar.css
+++ b/src/wp-includes/css/admin-bar.css
@@ -7,7 +7,7 @@
 	text-shadow: none;
 	text-transform: none;
 	letter-spacing: normal;
-	font: normal 13px/32px "Open Sans", sans-serif;
+	font: normal 13px/32px -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 	-webkit-border-radius: 0;
 	border-radius: 0;
 	-webkit-box-sizing: content-box;
@@ -79,7 +79,7 @@ html:lang(he-il) .rtl #wpadminbar *  {
 #wpadminbar {
 	direction: ltr;
 	color: #ccc;
-	font: normal 13px/32px "Open Sans", sans-serif;
+	font: normal 13px/32px -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 	height: 32px;
 	position: fixed;
 	top: 0;
@@ -618,7 +618,7 @@ html:lang(he-il) .rtl #wpadminbar *  {
 #wpadminbar > #wp-toolbar > #wp-admin-bar-top-secondary > #wp-admin-bar-search #adminbarsearch input.adminbar-input {
 	position: relative;
 	z-index: 30;
-	font: 13px/24px "Open Sans", sans-serif;
+	font: 13px/24px -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 	height: 24px;
 	width: 24px;
 	max-width: none;
@@ -798,7 +798,7 @@ html:lang(he-il) .rtl #wpadminbar *  {
 	}
 
 	#wpadminbar * {
-		font: normal 14px/32px "Open Sans", sans-serif;
+		font: normal 14px/32px -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif, sans-serif;
 	}
 
 	#wpadminbar .quicklinks > ul > li > a,
diff --git a/src/wp-includes/css/editor.css b/src/wp-includes/css/editor.css
index c2a036bb58..899cb3de84 100644
--- a/src/wp-includes/css/editor.css
+++ b/src/wp-includes/css/editor.css
@@ -1109,7 +1109,8 @@ i.mce-i-wp_code:before {
 	background: #ebebeb;
 	color: #666;
 	cursor: pointer;
-	font: 13px/19px "Open Sans", sans-serif;
+	font-size: 13px;
+	line-height: 19px;
 	height: 20px;
 	margin: 5px 0 0 5px;
 	padding: 3px 8px 4px;
diff --git a/src/wp-includes/css/media-views.css b/src/wp-includes/css/media-views.css
index 7f69a0edbd..313bf90904 100644
--- a/src/wp-includes/css/media-views.css
+++ b/src/wp-includes/css/media-views.css
@@ -17,7 +17,7 @@
 
 .media-modal,
 .media-frame {
-	font-family: "Open Sans", sans-serif;
+	font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 	font-size: 12px;
 	-webkit-overflow-scrolling: touch;
 }
@@ -80,7 +80,7 @@
 .media-frame input[type="url"],
 .media-frame textarea,
 .media-frame select {
-	font-family: "Open Sans", sans-serif;
+	font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 	font-size: 12px;
 	border-width: 1px;
 	border-style: solid;
@@ -807,7 +807,7 @@
 	padding: 4px;
 	font-size: 13px;
 	color: #444;
-	font-family: "Open Sans", sans-serif;
+	font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 	-webkit-appearance: none;
 }
 
diff --git a/src/wp-includes/css/wp-embed-template.css b/src/wp-includes/css/wp-embed-template.css
index d91bdb65f2..607d13f837 100644
--- a/src/wp-includes/css/wp-embed-template.css
+++ b/src/wp-includes/css/wp-embed-template.css
@@ -59,7 +59,7 @@ body {
 
 .wp-embed {
 	padding: 25px;
-	font: 400 14px/1.5 'Open Sans', sans-serif;
+	font: 400 14px/1.5 -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 	color: #82878c;
 	background: white;
 	border: 1px solid #e5e5e5;
@@ -307,7 +307,7 @@ p.wp-embed-share-description {
 	height: 28px;
 	margin: 0 0 10px 0;
 	padding: 0 5px;
-	font: 400 14px/1.5 'Open Sans', sans-serif;
+	font: 400 14px/1.5 -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 	resize: none;
 	cursor: text;
 }
diff --git a/src/wp-includes/embed.php b/src/wp-includes/embed.php
index 265d42acf6..bca5544ee2 100644
--- a/src/wp-includes/embed.php
+++ b/src/wp-includes/embed.php
@@ -877,7 +877,6 @@ function wp_embed_excerpt_attachment( $content ) {
  * @since 4.4.0
  */
 function enqueue_embed_scripts() {
-	wp_enqueue_style( 'open-sans' );
 	wp_enqueue_style( 'wp-embed-template-ie' );
 
 	/**
diff --git a/src/wp-includes/functions.php b/src/wp-includes/functions.php
index 7ce39cf9b4..d4731c0ab1 100644
--- a/src/wp-includes/functions.php
+++ b/src/wp-includes/functions.php
@@ -2667,7 +2667,7 @@ function _default_wp_die_handler( $message, $title = '', $args = array() ) {
 		body {
 			background: #fff;
 			color: #444;
-			font-family: "Open Sans", sans-serif;
+			font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 			margin: 2em auto;
 			padding: 1em 2em;
 			max-width: 700px;
@@ -2678,7 +2678,7 @@ function _default_wp_die_handler( $message, $title = '', $args = array() ) {
 			border-bottom: 1px solid #dadada;
 			clear: both;
 			color: #666;
-			font: 24px "Open Sans", sans-serif;
+			font-size: 24px;
 			margin: 30px 0 0 0;
 			padding: 0;
 			padding-bottom: 7px;
diff --git a/src/wp-includes/js/tinymce/plugins/compat3x/css/dialog.css b/src/wp-includes/js/tinymce/plugins/compat3x/css/dialog.css
index 02c0d294d2..c02f1be500 100644
--- a/src/wp-includes/js/tinymce/plugins/compat3x/css/dialog.css
+++ b/src/wp-includes/js/tinymce/plugins/compat3x/css/dialog.css
@@ -1,8 +1,6 @@
-@import url("https://fonts.googleapis.com/css?family=Open+Sans:300italic,400italic,600italic,300,400,600&subset=latin-ext,latin");
-
 /* Generic */
 body {
-font-family: "Open Sans", sans-serif;
+font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 font-size:13px;
 background:#fcfcfc;
 padding:0;
diff --git a/src/wp-includes/js/tinymce/skins/wordpress/wp-content.css b/src/wp-includes/js/tinymce/skins/wordpress/wp-content.css
index 39af33835f..80510aca8a 100644
--- a/src/wp-includes/js/tinymce/skins/wordpress/wp-content.css
+++ b/src/wp-includes/js/tinymce/skins/wordpress/wp-content.css
@@ -386,7 +386,7 @@ audio {
 .wpview-error p {
 	margin: 0;
 	text-align: center;
-	font-family: 'Open Sans', sans-serif;
+	font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen-Sans", "Ubuntu", "Cantarell", "Helvetica Neue", sans-serif;
 }
 
 .wpview-type-gallery:after {
diff --git a/src/wp-includes/script-loader.php b/src/wp-includes/script-loader.php
index fe9ab0a64f..a97bfe14c8 100644
--- a/src/wp-includes/script-loader.php
+++ b/src/wp-includes/script-loader.php
@@ -697,6 +697,7 @@ function wp_default_styles( &$styles ) {
 	$styles->text_direction = function_exists( 'is_rtl' ) && is_rtl() ? 'rtl' : 'ltr';
 	$styles->default_dirs = array('/wp-admin/', '/wp-includes/css/');
 
+	// Open Sans is no longer used by core, but may be relied upon by themes and plugins.
 	$open_sans_font_url = '';
 
 	/* translators: If there are characters in your language that are not supported
@@ -743,15 +744,15 @@ function wp_default_styles( &$styles ) {
 	$styles->add( 'site-icon',           "/wp-admin/css/site-icon$suffix.css" );
 	$styles->add( 'l10n',                "/wp-admin/css/l10n$suffix.css" );
 
-	$styles->add( 'wp-admin', false, array( 'open-sans', 'dashicons', 'common', 'forms', 'admin-menu', 'dashboard', 'list-tables', 'edit', 'revisions', 'media', 'themes', 'about', 'nav-menus', 'widgets', 'site-icon', 'l10n' ) );
+	$styles->add( 'wp-admin', false, array( 'dashicons', 'common', 'forms', 'admin-menu', 'dashboard', 'list-tables', 'edit', 'revisions', 'media', 'themes', 'about', 'nav-menus', 'widgets', 'site-icon', 'l10n' ) );
 
-	$styles->add( 'login',               "/wp-admin/css/login$suffix.css", array( 'open-sans', 'dashicons', 'buttons', 'forms', 'l10n' ) );
-	$styles->add( 'install',             "/wp-admin/css/install$suffix.css", array( 'open-sans', 'buttons' ) );
+	$styles->add( 'login',               "/wp-admin/css/login$suffix.css", array( 'dashicons', 'buttons', 'forms', 'l10n' ) );
+	$styles->add( 'install',             "/wp-admin/css/install$suffix.css", array( 'buttons' ) );
 	$styles->add( 'wp-color-picker',     "/wp-admin/css/color-picker$suffix.css" );
 	$styles->add( 'customize-controls',  "/wp-admin/css/customize-controls$suffix.css", array( 'wp-admin', 'colors', 'ie', 'imgareaselect' ) );
 	$styles->add( 'customize-widgets',   "/wp-admin/css/customize-widgets$suffix.css", array( 'wp-admin', 'colors' ) );
 	$styles->add( 'customize-nav-menus', "/wp-admin/css/customize-nav-menus$suffix.css", array( 'wp-admin', 'colors' ) );
-	$styles->add( 'press-this',          "/wp-admin/css/press-this$suffix.css", array( 'open-sans', 'buttons' ) );
+	$styles->add( 'press-this',          "/wp-admin/css/press-this$suffix.css", array( 'buttons' ) );
 
 	$styles->add( 'ie', "/wp-admin/css/ie$suffix.css" );
 	$styles->add_data( 'ie', 'conditional', 'lte IE 7' );
@@ -759,10 +760,9 @@ function wp_default_styles( &$styles ) {
 	// Common dependencies
 	$styles->add( 'buttons',   "/wp-includes/css/buttons$suffix.css" );
 	$styles->add( 'dashicons', "/wp-includes/css/dashicons$suffix.css" );
-	$styles->add( 'open-sans', $open_sans_font_url );
 
 	// Includes CSS
-	$styles->add( 'admin-bar',            "/wp-includes/css/admin-bar$suffix.css", array( 'open-sans', 'dashicons' ) );
+	$styles->add( 'admin-bar',            "/wp-includes/css/admin-bar$suffix.css", array( 'dashicons' ) );
 	$styles->add( 'wp-auth-check',        "/wp-includes/css/wp-auth-check$suffix.css", array( 'dashicons' ) );
 	$styles->add( 'editor-buttons',       "/wp-includes/css/editor$suffix.css", array( 'dashicons' ) );
 	$styles->add( 'media-views',          "/wp-includes/css/media-views$suffix.css", array( 'buttons', 'dashicons', 'wp-mediaelement' ) );
@@ -783,6 +783,7 @@ function wp_default_styles( &$styles ) {
 	$styles->add( 'farbtastic',       "/wp-admin/css/farbtastic$suffix.css", array(), '1.3u1' );
 	$styles->add( 'jcrop',            "/wp-includes/js/jcrop/jquery.Jcrop.min.css", array(), '0.9.12' );
 	$styles->add( 'colors-fresh', false, array( 'wp-admin', 'buttons' ) ); // Old handle.
+	$styles->add( 'open-sans', $open_sans_font_url ); // No longer used in core as of 4.6
 
 	// RTL CSS
 	$rtl_styles = array(