diff --git a/README.md b/README.md
index 03793c9..01e0ce7 100644
--- a/README.md
+++ b/README.md
@@ -189,6 +189,7 @@ Name | Action | Tooltip<br>Class
 bold | toggleBold | Bold<br>fa fa-bold
 italic | toggleItalic | Italic<br>fa fa-italic
 strikethrough | toggleStrikethrough | Strikethrough<br>fa fa-strikethrough
+underline | toggleUnderline | Underline<br>fa fa-underline
 heading | toggleHeadingSmaller | Heading<br>fa fa-header
 heading-smaller | toggleHeadingSmaller | Smaller Heading<br>fa fa-header
 heading-bigger | toggleHeadingBigger | Bigger Heading<br>fa fa-lg fa-header
@@ -247,6 +248,7 @@ Shortcut | Action
 :------- | :-----
 *Cmd-'* | "toggleBlockquote"
 *Cmd-B* | "toggleBold"
+*Cmd-U* | "toggleUnderline"
 *Cmd-E* | "cleanBlock"
 *Cmd-H* | "toggleHeadingSmaller"
 *Cmd-I* | "toggleItalic"
diff --git a/src/js/simplemde.js b/src/js/simplemde.js
index 016d693..426b00d 100644
--- a/src/js/simplemde.js
+++ b/src/js/simplemde.js
@@ -21,6 +21,7 @@ var isMac = /Mac/.test(navigator.platform);
 var bindings = {
 	"toggleBold": toggleBold,
 	"toggleItalic": toggleItalic,
+	"toggleUnderline": toggleUnderline,
 	"drawLink": drawLink,
 	"toggleHeadingSmaller": toggleHeadingSmaller,
 	"toggleHeadingBigger": toggleHeadingBigger,
@@ -46,6 +47,7 @@ var bindings = {
 var shortcuts = {
 	"toggleBold": "Cmd-B",
 	"toggleItalic": "Cmd-I",
+	"toggleUnderline": "Cmd-U",
 	"drawLink": "Cmd-K",
 	"toggleHeadingSmaller": "Cmd-H",
 	"toggleHeadingBigger": "Shift-Cmd-H",
@@ -242,6 +244,12 @@ function toggleItalic(editor) {
 	_toggleBlock(editor, "italic", editor.options.blockStyles.italic);
 }
 
+/**
+ * Action for toggling underline.
+ */
+function toggleUnderline(editor) {
+	_toggleBlock(editor, "underline", "__");
+}
 
 /**
  * Action for toggling strikethrough.
@@ -1081,6 +1089,12 @@ var toolbarBuiltInButtons = {
 		title: "Italic",
 		default: true
 	},
+	"underline": {
+		name: "underline",
+		action: toggleUnderline,
+		className: "fa fa-underline",
+		title: "Underline"
+	},
 	"strikethrough": {
 		name: "strikethrough",
 		action: toggleStrikethrough,
@@ -1881,6 +1895,7 @@ SimpleMDE.prototype.value = function(val) {
  */
 SimpleMDE.toggleBold = toggleBold;
 SimpleMDE.toggleItalic = toggleItalic;
+SimpleMDE.toggleUnderline = toggleUnderline;
 SimpleMDE.toggleStrikethrough = toggleStrikethrough;
 SimpleMDE.toggleBlockquote = toggleBlockquote;
 SimpleMDE.toggleHeadingSmaller = toggleHeadingSmaller;
@@ -1911,6 +1926,9 @@ SimpleMDE.prototype.toggleBold = function() {
 SimpleMDE.prototype.toggleItalic = function() {
 	toggleItalic(this);
 };
+SimpleMDE.prototype.toggleUnderline = function() {
+	toggleUnderline(this);
+};
 SimpleMDE.prototype.toggleStrikethrough = function() {
 	toggleStrikethrough(this);
 };
@@ -2025,4 +2043,4 @@ SimpleMDE.prototype.toTextArea = function() {
 	}
 };
 
-module.exports = SimpleMDE;
\ No newline at end of file
+module.exports = SimpleMDE;