diff --git a/Makefile b/Makefile
index 2274e81ee4..96de83b3d0 100644
--- a/Makefile
+++ b/Makefile
@@ -55,6 +55,8 @@ publish:
 	make build
 	cp dist/6to5.js browser.js
 
+	node bin/6to5-runtime >runtime.js
+
 	node bin/cache-templates
 	test -f templates.json
 
@@ -64,4 +66,4 @@ publish:
 
 	git push --follow-tags
 
-	rm -rf templates.json browser.js
+	rm -rf templates.json browser.js runtime.js
diff --git a/README.md b/README.md
index f58af6a14b..d01ec44642 100644
--- a/README.md
+++ b/README.md
@@ -43,6 +43,7 @@ It's as easy as:
   - [Browser](#browser)
 - [Modules](#modules)
 - [Caveats](#caveats)
+- [Runtime](#runtime)
 - [Differences](#differences)
 
 ## [Features](FEATURES.md)
@@ -177,7 +178,12 @@ to5.transformFile("filename.js", options, function (err, result) {
 
   // Set `sources[0]` on returned source map.
   // Default: `filename` option.
-  sourceFileName: "filename"
+  sourceFileName: "filename",
+
+  // Optionally replace all 6to5 helper declarations with a referenece to this
+  // variable. If set to `true` then the default namespace is used "to5Runtime".
+  // Default: false
+  runtime: true
 }
 ```
 
@@ -226,6 +232,33 @@ require("6to5/register")({
 
 ### Browser
 
+A browser version of 6to5 is available from `browser.js` inside the 6to5
+directory in an npm release.
+
+#### Scripts
+
+While it's not recommended for serious use, when the browser version is included
+all scripts with the type `text/ecmascript-6` and `text/6to5` are automatically
+compiled and ran.
+
+For example:
+
+```html
+<script src="node_modules/6to5/browser.js"></script>
+<script type="text/6to5">
+class Test {
+  test() {
+    return "test";
+  }
+}
+
+var test = new Test;
+test.test();
+</script>
+```
+
+#### Build
+
 You can build a browser version of the compiler by running the following in the
 6to5 directory:
 
@@ -233,8 +266,7 @@ You can build a browser version of the compiler by running the following in the
 
 This will output the files `dist/6to5.js` and `dist/6to5.min.js`.
 
-Just include one of those in the browser and access the transform method via the
-global `to5`.
+#### API
 
 ```javascript
 to5.transform("class Test {}").code;
@@ -320,6 +352,58 @@ class Bar extends Foo {
 The [regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js)
 and an [ES6 polyfill](#polyfill) are required in order for generators to work.
 
+## Runtime
+
+6to5 has a few helper functions that'll be placed at the top of the generated
+code so it's not inlined multiple times throughout that file. This may become an
+issue if you have multiple files, especially when you're sending them to the
+browser. gzip alleviates most of this concern but it's still not ideal.
+
+You can tell 6to5 to not place any declarations at the top of your files and
+instead just point them to a reference contained within the runtime.
+
+Simply use the following option if you're using the [Node API](#node-1):
+
+```javascript
+{
+  runtime: true
+}
+```
+
+or the following flag if you're using the [CLI](#cli):
+
+    $ 6to5 --runtime
+
+Then just include the runtime before your generated code.
+
+### Getting the runtime
+
+You can get the runtime via either:
+
+    $ 6to5-runtime
+
+or
+
+```javascript
+require("6to5").runtime();
+```
+
+or from an npm release in `runtime.js` from the 6to5 directory.
+
+### Customising namespace
+
+You can also customise the runtime namespace by passing an optional namespace
+argument:
+
+```javascript
+require("6to5").runtime("myCustomNamespace");
+```
+
+    $ 6to5-runtime myCustomNamespace
+
+See [Options - runtime](#options) for documentation on changing the reference in
+generated code.
+
 ## Differences
 
 ### Philosophy
diff --git a/bin/6to5-runtime b/bin/6to5-runtime
new file mode 100755
index 0000000000..a19e68f826
--- /dev/null
+++ b/bin/6to5-runtime
@@ -0,0 +1,4 @@
+#!/usr/bin/env node
+
+var runtime = require("../lib/6to5/runtime");
+console.log(runtime(process.argv[2]));
diff --git a/bin/6to5/index.js b/bin/6to5/index.js
index a3991603f4..b492dbb1b7 100755
--- a/bin/6to5/index.js
+++ b/bin/6to5/index.js
@@ -10,6 +10,7 @@ commander.option("-t, --source-maps-inline", "Append sourceMappingURL comment to
 commander.option("-s, --source-maps", "Save source map alongside the compiled code");
 commander.option("-f, --filename [filename]", "Filename to use when reading from stdin - this will be used in source-maps, errors etc [stdin]", "stdin");
 commander.option("-w, --watch", "Recompile files on changes");
+commander.option("-r, --runtime", "Replace 6to5 declarations with references to a runtime");
 
 commander.option("-m, --modules [modules]", "Module formatter type to use [common]", "common");
 commander.option("-w, --whitelist [whitelist]", "Whitelist of transformers to ONLY use", util.list);
@@ -87,6 +88,7 @@ exports.opts = {
   blacklist:     commander.blacklist,
   whitelist:     commander.whitelist,
   sourceMap:     commander.sourceMaps || commander.sourceMapsInline,
+  runtime:       commander.runtime,
   modules:       commander.modules
 };
 
diff --git a/lib/6to5/file.js b/lib/6to5/file.js
index 9bbf157cf8..9e8d6a674b 100644
--- a/lib/6to5/file.js
+++ b/lib/6to5/file.js
@@ -5,7 +5,6 @@ var SHEBANG_REGEX = /^\#\!.*/;
 var transform = require("./transformation/transform");
 var generate  = require("./generation/generator");
 var Scope     = require("./traverse/scope");
-var acorn     = require("acorn-6to5");
 var util      = require("./util");
 var t         = require("./types");
 var _         = require("lodash");
@@ -19,6 +18,8 @@ function File(opts) {
   this.ast          = {};
 }
 
+File.declarations = ["extends", "class-props", "slice"];
+
 File.normaliseOptions = function (opts) {
   opts = opts || {};
 
@@ -28,7 +29,8 @@ File.normaliseOptions = function (opts) {
     whitelist:  [],
     sourceMap:  false,
     filename:   "unknown",
-    modules:    "common"
+    modules:    "common",
+    runtime:    false
   });
 
   _.defaults(opts, {
@@ -36,6 +38,10 @@ File.normaliseOptions = function (opts) {
     sourceMapName:  opts.filename
   });
 
+  if (opts.runtime === true) {
+    opts.runtime = "to5Runtime";
+  }
+
   transform._ensureTransformerNames("blacklist", opts.blacklist);
   transform._ensureTransformerNames("whitelist", opts.whitelist);
 
@@ -43,18 +49,18 @@ File.normaliseOptions = function (opts) {
 };
 
 File.prototype.getModuleFormatter = function (type) {
-  var ModuleLoader = transform.moduleFormatters[type];
+  var ModuleFormatter = transform.moduleFormatters[type];
 
-  if (!ModuleLoader) {
+  if (!ModuleFormatter) {
     var loc = util.resolve(type);
-    if (loc) ModuleLoader = require(loc);
+    if (loc) ModuleFormatter = require(loc);
   }
 
-  if (!ModuleLoader) {
+  if (!ModuleFormatter) {
     throw new ReferenceError("unknown module formatter type " + type);
   }
 
-  return new ModuleLoader(this);
+  return new ModuleFormatter(this);
 };
 
 File.prototype.parseShebang = function (code) {
@@ -70,13 +76,26 @@ File.prototype.parseShebang = function (code) {
 };
 
 File.prototype.addDeclaration = function (name) {
+  if (!_.contains(File.declarations, name)) {
+    throw new ReferenceError("unknown declaration " + name);
+  }
+
   var declar = this.declarations[name];
   if (declar) return declar.uid;
 
+  var ref;
+  var runtimeNamespace = this.opts.runtime;
+  if (runtimeNamespace) {
+    name = t.identifier(t.toIdentifier(name));
+    return t.memberExpression(t.identifier(runtimeNamespace), name);
+  } else {
+    ref = util.template(name);
+  }
+
   var uid = t.identifier(this.generateUid(name));
   this.declarations[name] = {
     uid: uid,
-    node: util.template(name)
+    node: ref
   };
   return uid;
 };
@@ -118,7 +137,7 @@ File.prototype.generate = function () {
   var opts = this.opts;
   var ast  = this.ast;
 
-  var result = generate(this.code, ast, opts);
+  var result = generate(ast, opts, this.code);
 
   if (this.shebang) {
     // add back shebang
@@ -133,7 +152,10 @@ File.prototype.generate = function () {
 };
 
 File.prototype.generateUid = function (name, scope) {
+  name = t.toIdentifier(name);
+
   scope = scope || this.scope;
+
   var uid;
   do {
     uid = this._generateUid(name);
@@ -142,17 +164,6 @@ File.prototype.generateUid = function (name, scope) {
 };
 
 File.prototype._generateUid = function (name) {
-  // replace all non-valid identifiers with dashes
-  name = name.replace(/[^a-zA-Z0-9]/g, "-");
-
-  // remove all dashes and numbers from start of name
-  name = name.replace(/^[-0-9]+/, "");
-
-  // camel case
-  name = name.replace(/[-_\s]+(.)?/g, function (match, c) {
-    return c ? c.toUpperCase() : "";
-  });
-
   var uids = this.uids;
   var i = uids[name] || 1;
 
diff --git a/lib/6to5/index.js b/lib/6to5/index.js
index c1b0a2db3a..29e73fc64c 100644
--- a/lib/6to5/index.js
+++ b/lib/6to5/index.js
@@ -2,6 +2,8 @@ var transform = require("./transformation/transform");
 var fs        = require("fs");
 var _         = require("lodash");
 
+exports.runtime = require("./runtime");
+
 exports.register = function (opts) {
   var register = require("./register");
   if (opts != null) register(opts);
diff --git a/lib/6to5/runtime.js b/lib/6to5/runtime.js
new file mode 100644
index 0000000000..ee77d65c60
--- /dev/null
+++ b/lib/6to5/runtime.js
@@ -0,0 +1,44 @@
+var generator = require("./generation/generator");
+var util      = require("./util");
+var File      = require("./file");
+var t         = require("./types");
+var _         = require("lodash");
+
+module.exports = function (namespace) {
+  var body = [];
+  var container = t.functionExpression(null, [], t.blockStatement(body));
+
+  var tree = {
+    type: "Program",
+    body: [t.expressionStatement(t.callExpression(container, []))]
+  };
+
+  body.push(t.variableDeclaration("var", [
+    t.variableDeclarator(t.identifier("self"), t.conditionalExpression(
+      t.binaryExpression("===",
+        t.unaryExpression("typeof", t.identifier("global"), true),
+        t.literal("undefined")
+      ),
+      t.identifier("window"),
+      t.identifier("global"))
+    )
+  ]));
+
+  var namespace = t.identifier(namespace || "to5Runtime");
+
+  body.push(t.variableDeclaration("var", [
+    t.variableDeclarator(
+      namespace,
+      t.assignmentExpression("=", t.memberExpression(t.identifier("self"), namespace), t.objectExpression([]))
+    )
+  ]));
+
+  _.each(File.declarations, function (name) {
+    var key = t.identifier(t.toIdentifier(name));
+    body.push(t.expressionStatement(
+      t.assignmentExpression("=", t.memberExpression(namespace, key), util.template(name))
+    ));
+  });
+
+  return generator(tree).code;
+};
diff --git a/package.json b/package.json
index cf7bac9c35..53a7c7220b 100644
--- a/package.json
+++ b/package.json
@@ -15,7 +15,8 @@
   "main": "lib/6to5/index.js",
   "bin": {
     "6to5": "./bin/6to5/index.js",
-    "6to5-node": "./bin/6to5-node"
+    "6to5-node": "./bin/6to5-node",
+    "6to5-runtime": "./bin/6to5-runtime"
   },
   "keywords": [
     "harmony",