diff --git a/demo/kitchen-sink/docs/lean.lean b/demo/kitchen-sink/docs/lean.lean
new file mode 100644
index 00000000..40e82753
--- /dev/null
+++ b/demo/kitchen-sink/docs/lean.lean
@@ -0,0 +1,9 @@
+import logic
+section
+  variables (A : Type) (p q : A → Prop)
+
+  example : (∀x : A, p x ∧ q x) → ∀y : A, p y  :=
+  assume H : ∀x : A, p x ∧ q x,
+  take y : A,
+  show p y, from and.elim_left (H y)
+end
diff --git a/lib/ace/ext/modelist.js b/lib/ace/ext/modelist.js
index 69aa8972..fba3a245 100644
--- a/lib/ace/ext/modelist.js
+++ b/lib/ace/ext/modelist.js
@@ -99,6 +99,7 @@ var supportedModes = {
     JSX:         ["jsx"],
     Julia:       ["jl"],
     LaTeX:       ["tex|latex|ltx|bib"],
+    Lean:        ["lean|hlean"],
     LESS:        ["less"],
     Liquid:      ["liquid"],
     Lisp:        ["lisp"],
@@ -192,4 +193,3 @@ module.exports = {
 };
 
 });
-
diff --git a/lib/ace/mode/lean.js b/lib/ace/mode/lean.js
new file mode 100644
index 00000000..e421f2b5
--- /dev/null
+++ b/lib/ace/mode/lean.js
@@ -0,0 +1,101 @@
+/* ***** BEGIN LICENSE BLOCK *****
+ * Distributed under the BSD license:
+ *
+ * Copyright (c) 2010, Ajax.org B.V.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *     * Neither the name of Ajax.org B.V. nor the
+ *       names of its contributors may be used to endorse or promote products
+ *       derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL AJAX.ORG B.V. BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * ***** END LICENSE BLOCK ***** */
+
+define(function(require, exports, module) {
+"use strict";
+
+var oop = require("../lib/oop");
+var TextMode = require("./text").Mode;
+var leanHighlightRules = require("./lean_highlight_rules").leanHighlightRules;
+var MatchingBraceOutdent = require("./matching_brace_outdent").MatchingBraceOutdent;
+var Range = require("../range").Range;
+// TODO(soonhok): figure out behavior and foldmode
+// var CstyleBehaviour = require("./behaviour/cstyle").CstyleBehaviour;
+// var CStyleFoldMode = require("./folding/cstyle").FoldMode;
+
+var Mode = function() {
+    this.HighlightRules = leanHighlightRules;
+
+    this.$outdent = new MatchingBraceOutdent();
+    // this.$behaviour = new CstyleBehaviour();
+    // this.foldingRules = new CStyleFoldMode();
+};
+oop.inherits(Mode, TextMode);
+
+(function() {
+
+    this.lineCommentStart = "--";
+    this.blockComment = {start: "/-", end: "-/"};
+
+    this.getNextLineIndent = function(state, line, tab) {
+        var indent = this.$getIndent(line);
+
+        var tokenizedLine = this.getTokenizer().getLineTokens(line, state);
+        var tokens = tokenizedLine.tokens;
+        var endState = tokenizedLine.state;
+
+        if (tokens.length && tokens[tokens.length-1].type == "comment") {
+            return indent;
+        }
+
+        if (state == "start") {
+            var match = line.match(/^.*[\{\(\[]\s*$/);
+            if (match) {
+                indent += tab;
+            }
+        } else if (state == "doc-start") {
+            if (endState == "start") {
+                return "";
+            }
+            var match = line.match(/^\s*(\/?)\*/);
+            if (match) {
+                if (match[1]) {
+                    indent += " ";
+                }
+                indent += "- ";
+            }
+        }
+
+        return indent;
+    };
+
+    this.checkOutdent = function(state, line, input) {
+        return this.$outdent.checkOutdent(line, input);
+    };
+
+    this.autoOutdent = function(state, doc, row) {
+        this.$outdent.autoOutdent(doc, row);
+    };
+
+    this.$id = "ace/mode/lean";
+}).call(Mode.prototype);
+
+exports.Mode = Mode;
+});
diff --git a/lib/ace/mode/lean_highlight_rules.js b/lib/ace/mode/lean_highlight_rules.js
new file mode 100644
index 00000000..d4a37d20
--- /dev/null
+++ b/lib/ace/mode/lean_highlight_rules.js
@@ -0,0 +1,156 @@
+/* ***** BEGIN LICENSE BLOCK *****
+ * Distributed under the BSD license:
+ *
+ * Copyright (c) 2010, Ajax.org B.V.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *     * Neither the name of Ajax.org B.V. nor the
+ *       names of its contributors may be used to endorse or promote products
+ *       derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL AJAX.ORG B.V. BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * ***** END LICENSE BLOCK ***** */
+
+define(function(require, exports, module) {
+"use strict";
+
+var oop = require("../lib/oop");
+var DocCommentHighlightRules = require("./doc_comment_highlight_rules").DocCommentHighlightRules;
+var TextHighlightRules = require("./text_highlight_rules").TextHighlightRules;
+
+var leanHighlightRules = function() {
+
+    var keywordControls = (
+        [ "add_rewrite", "alias", "as", "assume", "attribute",
+          "begin", "by", "calc", "calc_refl", "calc_subst", "calc_trans", "check",
+          "classes", "coercions", "conjecture", "constants", "context",
+          "corollary", "else", "end", "environment", "eval", "example",
+          "exists", "exit", "export", "exposing", "extends", "fields", "find_decl",
+          "forall", "from", "fun", "have", "help", "hiding", "if",
+          "import", "in", "infix", "infixl", "infixr", "instances",
+          "let", "local", "match", "namespace", "notation", "obtain", "obtains",
+          "omit", "opaque", "open", "options", "parameter", "parameters", "postfix",
+          "precedence", "prefix", "premise", "premises", "print", "private", "proof",
+          "protected", "qed", "raw", "renaming", "section", "set_option",
+          "show", "tactic_hint", "take", "then", "universe",
+          "universes", "using", "variable", "variables", "with"].join("|")
+    );
+
+    var nameProviders = (
+        ["inductive", "structure", "record", "theorem", "axiom",
+         "axioms", "lemma", "hypothesis", "definition", "constant"].join("|")
+    );
+
+    var storageType = (
+        ["Prop", "Type", "Type'", "Type₊", "Type₁", "Type₂", "Type₃"].join("|")
+    );
+
+    var storageModifiers = (
+        "\\[(" +
+            ["abbreviations", "all-transparent", "begin-end-hints", "class", "classes", "coercion",
+             "coercions", "declarations", "decls", "instance", "irreducible",
+             "multiple-instances", "notation", "notations", "parsing-only", "persistent",
+             "reduce-hints", "reducible", "tactic-hints", "visible", "wf", "whnf"
+            ].join("|") +
+            ")\\]"
+    );
+
+    var keywordOperators = (
+        [].join("|")
+    );
+
+    var keywordMapper = this.$keywords = this.createKeywordMapper({
+        "keyword.control" : keywordControls,
+        "storage.type" : storageType,
+        "keyword.operator" : keywordOperators,
+        "variable.language": "sorry",
+    }, "identifier");
+
+    var identifierRe = "[A-Za-z_\u03b1-\u03ba\u03bc-\u03fb\u1f00-\u1ffe\u2100-\u214f][A-Za-z0-9_'\u03b1-\u03ba\u03bc-\u03fb\u1f00-\u1ffe\u2070-\u2079\u207f-\u2089\u2090-\u209c\u2100-\u214f]*";
+    var operatorRe = new RegExp(["#", "@", "->", "∼", "↔", "/", "==", "=", ":=", "<->",
+                                 "/\\", "\\/", "∧", "∨", "≠", "<", ">", "≤", "≥", "¬",
+                                 "<=", ">=", "⁻¹", "⬝", "▸", "\\+", "\\*", "-", "/",
+                                 "λ", "→", "∃", "∀", ":="].join("|"));
+    // regexp must not have capturing parentheses. Use (?:) instead.
+    // regexps are ordered -> the first match is used
+
+    this.$rules = {
+        "start" : [
+            {
+                token : "comment", // single line comment "--"
+                regex : "--.*$"
+            },
+            DocCommentHighlightRules.getStartRule("doc-start"),
+            {
+                token : "comment", // multi line comment "/-"
+                regex : "\\/-",
+                next : "comment"
+            }, {
+                stateName: "qqstring",
+                token : "string.start", regex : '"', next : [
+                    {token : "string.end", regex : '"', next : "start"},
+                    {token : "constant.language.escape", regex : /\\[n"\\]/},
+                    {defaultToken: "string"}
+                ]
+            }, {
+                token : "keyword.control", regex : nameProviders, next : [
+                    {token : "variable.language", regex : identifierRe, next : "start"} ]
+            }, {
+                token : "constant.numeric", // hex
+                regex : "0[xX][0-9a-fA-F]+(L|l|UL|ul|u|U|F|f|ll|LL|ull|ULL)?\\b"
+            }, {
+                token : "constant.numeric", // float
+                regex : "[+-]?\\d+(?:(?:\\.\\d*)?(?:[eE][+-]?\\d+)?)?(L|l|UL|ul|u|U|F|f|ll|LL|ull|ULL)?\\b"
+            }, {
+                token : "storage.modifier",
+                regex : storageModifiers
+            }, {
+                token : keywordMapper,
+                regex : identifierRe
+            }, {
+                token : "operator",
+                regex : operatorRe
+            }, {
+              token : "punctuation.operator",
+              regex : "\\?|\\:|\\,|\\;|\\."
+            }, {
+                token : "paren.lparen",
+                regex : "[[({]"
+            }, {
+                token : "paren.rparen",
+                regex : "[\\])}]"
+            }, {
+                token : "text",
+                regex : "\\s+"
+            }
+        ],
+        "comment" : [ {token: "comment", regex: "-/", next: "start"},
+                      {defaultToken: "comment"} ]
+    };
+
+    this.embedRules(DocCommentHighlightRules, "doc-",
+        [ DocCommentHighlightRules.getEndRule("start") ]);
+    this.normalizeRules();
+};
+
+oop.inherits(leanHighlightRules, TextHighlightRules);
+
+exports.leanHighlightRules = leanHighlightRules;
+});
diff --git a/lib/ace/snippets/lean.js b/lib/ace/snippets/lean.js
new file mode 100644
index 00000000..a3c01639
--- /dev/null
+++ b/lib/ace/snippets/lean.js
@@ -0,0 +1,7 @@
+define(function(require, exports, module) {
+"use strict";
+
+exports.snippetText = require("../requirejs/text!./lean.snippets");
+exports.scope = "lean";
+
+});
diff --git a/lib/ace/snippets/lean.snippets b/lib/ace/snippets/lean.snippets
new file mode 100644
index 00000000..e69de29b