diff --git a/MIT-LICENSE b/MIT-LICENSE
new file mode 100644
index 000000000..9fded7b4e
--- /dev/null
+++ b/MIT-LICENSE
@@ -0,0 +1,20 @@
+Copyright (c) 2016 David Heinemeier Hansson, Basecamp
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
diff --git a/README.md b/README.md
new file mode 100644
index 000000000..9b2de095c
--- /dev/null
+++ b/README.md
@@ -0,0 +1,18 @@
+# Webpacker
+
+Webpacker makes it easy to use the JavaScript preprocessor and bundler Webpack
+to manage application-like JavaScript in Rails. It coexists with the asset pipeline,
+as the purpose is only to use Webpack for app-like JavaScript, not images, css, or
+even JavaScript Sprinkles.
+
+It's designed to work with Rails 5.1+ and makes use of the Yarn dependency management
+that's been made default from that version forward. You can either make use of Webpacker
+during setup of a new application with --webpack or you can uncomment the gem and run
+`bin/rails webpacker:install` in an existing application.
+
+When Webpacker has been installed...
+
+FIXME: Write the rest...
+
+## License
+Webpacker is released under the [MIT License](http://www.opensource.org/licenses/MIT).
diff --git a/lib/install/bin/webpack-watcher.tt b/lib/install/bin/webpack-watcher.tt
new file mode 100644
index 000000000..ce6e91c67
--- /dev/null
+++ b/lib/install/bin/webpack-watcher.tt
@@ -0,0 +1,7 @@
+<%= shebang %>
+
+BIN_PATH = File.expand_path('.', __dir__)
+
+Dir.chdir(BIN_PATH) do
+  exec "./webpack --watch --progress --color #{ARGV.join(" ")}"
+end
diff --git a/lib/install/bin/webpack.tt b/lib/install/bin/webpack.tt
new file mode 100644
index 000000000..c087a589d
--- /dev/null
+++ b/lib/install/bin/webpack.tt
@@ -0,0 +1,15 @@
+<%= shebang %>
+
+RAILS_ENV   = ENV['RAILS_ENV'] || 'development'
+WEBPACK_ENV = ENV['WEBPACK_ENV'] || RAILS_ENV
+
+APP_PATH    = File.expand_path('../', __dir__)
+VENDOR_PATH = File.expand_path('../vendor', __dir__)
+
+SET_NODE_PATH  = "NODE_PATH=#{VENDOR_PATH}/node_modules"
+WEBPACK_BIN    = "./node_modules/webpack/bin/webpack.js"
+WEBPACK_CONFIG = "#{APP_PATH}/config/webpack/#{WEBPACK_ENV}.js"
+
+Dir.chdir(VENDOR_PATH) do
+  exec "#{SET_NODE_PATH} #{WEBPACK_BIN} --config #{WEBPACK_CONFIG} #{ARGV.join(" ")}"
+end
diff --git a/lib/install/config/development.js b/lib/install/config/development.js
new file mode 100644
index 000000000..0188b9213
--- /dev/null
+++ b/lib/install/config/development.js
@@ -0,0 +1,14 @@
+// Note: You must restart bin/webpack-watcher for changes to take effect
+
+var path    = require('path')
+var webpack = require('webpack')
+var _       = require('lodash')
+
+var config = module.exports = require('./shared.js')
+
+config = _.merge(config, {
+  debug: true,
+  displayErrorDetails: true,
+  outputPathinfo: true,
+  devtool: 'sourcemap',
+})
diff --git a/lib/install/config/production.js b/lib/install/config/production.js
new file mode 100644
index 000000000..aaeb8d6d8
--- /dev/null
+++ b/lib/install/config/production.js
@@ -0,0 +1,14 @@
+// Note: You must restart bin/webpack-watcher for changes to take effect
+
+var path    = require('path')
+var webpack = require('webpack')
+var _       = require('lodash')
+
+var config = module.exports = require('./shared.js');
+
+config.output = _.merge(config.output, { filename: '[name]-[hash].js' })
+
+config.plugins.push(
+  new webpack.optimize.UglifyJsPlugin(),
+  new webpack.optimize.OccurenceOrderPlugin()
+)
diff --git a/lib/install/config/shared.js b/lib/install/config/shared.js
new file mode 100644
index 000000000..d14925675
--- /dev/null
+++ b/lib/install/config/shared.js
@@ -0,0 +1,31 @@
+// Note: You must restart bin/webpack-watcher for changes to take effect
+
+var path = require('path')
+var glob = require('glob')
+var _    = require('lodash')
+
+module.exports = {
+  entry: _.keyBy(glob.sync('../app/javascript/packs/*.js'), function(entry) { return path.basename(entry, '.js') }),
+
+  output: { filename: '[name].js', path: '../public/packs' },
+
+  module: {
+    loaders: [
+      { test: /\.coffee$/, loader: "coffee-loader" }
+    ]
+  },
+
+  plugins: [],
+
+  resolve: {
+    extensions: [ '', '.js', '.coffee' ],
+    root: [
+      path.resolve('../app/javascript'),
+      path.resolve('../vendor/node_modules')
+    ]
+  },
+
+  resolveLoader: {
+    modulesDirectories: [ path.resolve('../vendor/node_modules') ]
+  }
+}
diff --git a/lib/install/javascript/packs/application.js b/lib/install/javascript/packs/application.js
new file mode 100644
index 000000000..56b1f64d1
--- /dev/null
+++ b/lib/install/javascript/packs/application.js
@@ -0,0 +1 @@
+// var React = require('react')
diff --git a/lib/install/template.rb b/lib/install/template.rb
new file mode 100644
index 000000000..47e2d977b
--- /dev/null
+++ b/lib/install/template.rb
@@ -0,0 +1,15 @@
+INSTALL_PATH = File.dirname(__FILE__)
+
+directory "#{INSTALL_PATH}/javascript", 'app/javascript'
+
+directory "#{INSTALL_PATH}/bin", 'bin'
+chmod 'bin', 0755 & ~File.umask, verbose: false
+
+directory "#{INSTALL_PATH}/config", 'config/webpack'
+
+run './bin/yarn add webpack lodash'
+
+environment \
+  "# Make javascript_pack_tag lookup digest hash to enable long-term caching\n" +
+  "  config.x.webpacker[:digesting] = true\n",
+  env: 'production'
diff --git a/lib/tasks/webpacker.rake b/lib/tasks/webpacker.rake
new file mode 100644
index 000000000..93e78784b
--- /dev/null
+++ b/lib/tasks/webpacker.rake
@@ -0,0 +1,22 @@
+PACKS_PATH        = Rails.root.join('public/packs')
+PACK_DIGESTS_PATH = PACKS_PATH.join('digests.json')
+
+WEBPACKER_APP_TEMPLATE_PATH = File.expand_path('../install/template.rb', File.dirname(__FILE__))
+
+namespace :webpacker do
+  desc "compile javascript packs using webpack for production with digests"
+  task :compile do
+    webpack_digests_json = JSON.parse(`WEBPACK_ENV=production ./bin/webpack --json`)['assetsByChunkName'].to_json
+
+    FileUtils.mkdir_p(PACKS_PATH)
+    File.open(PACK_DIGESTS_PATH, 'w+') { |file| file.write webpack_digests_json }
+
+    puts "Compiled digests for all packs in #{PACK_DIGESTS_PATH}: "
+    puts webpack_digests_json
+  end
+
+  desc "install webpacker in this application"
+  task :install do
+    exec "./bin/rails app:template LOCATION=#{WEBPACKER_APP_TEMPLATE_PATH}"
+  end
+end
diff --git a/lib/webpacker.rb b/lib/webpacker.rb
new file mode 100644
index 000000000..463f2ee7b
--- /dev/null
+++ b/lib/webpacker.rb
@@ -0,0 +1,4 @@
+module Webpacker
+end
+
+require 'webpacker/railtie' if defined?(Rails)
diff --git a/lib/webpacker/digests.rb b/lib/webpacker/digests.rb
new file mode 100644
index 000000000..0b1519cb9
--- /dev/null
+++ b/lib/webpacker/digests.rb
@@ -0,0 +1,36 @@
+class Webpacker::Digests
+  class_attribute :instance
+
+  class << self
+    def load(path)
+      self.instance = new(path)
+    end
+
+    def lookup(name)
+      if instance
+        instance.lookup(name)
+      else
+        raise "Webpacker::Digests.load(path) must be called first"
+      end
+    end
+  end
+
+  def initialize(path)
+    @path = path
+    load
+  end
+
+  def lookup(name)
+    @digests[name.to_s]
+  end
+
+  private
+    def load
+      begin
+        @digests = JSON.parse(File.read(@path))
+      rescue Errno::ENOENT
+        Rails.logger.error \
+          "Missing digests file at #{@path}! You must first compile the packs via rails webpacker:compile"
+      end
+    end
+end
diff --git a/lib/webpacker/helper.rb b/lib/webpacker/helper.rb
new file mode 100644
index 000000000..dbabd2296
--- /dev/null
+++ b/lib/webpacker/helper.rb
@@ -0,0 +1,7 @@
+require 'webpacker/source'
+
+module Webpacker::Helper
+  def javascript_pack_tag(name, **options)
+    tag.script src: Webpacker::Source.new(name).path, **options
+  end
+end
diff --git a/lib/webpacker/railtie.rb b/lib/webpacker/railtie.rb
new file mode 100644
index 000000000..1b9b2d1c6
--- /dev/null
+++ b/lib/webpacker/railtie.rb
@@ -0,0 +1,18 @@
+require 'rails/railtie'
+
+require 'webpacker/helper'
+require 'webpacker/digests'
+
+class Webpacker::Engine < ::Rails::Engine
+  initializer :webpacker do
+    ActiveSupport.on_load :action_controller do
+      ActionController::Base.helper Webpacker::Helper
+    end
+
+    if Rails.configuration.x.webpacker[:digesting]
+      Webpacker::Digests.load \
+        Rails.application.config.x.webpacker[:digests_path] ||
+          Rails.root.join('public/packs/digests.json')
+    end
+  end
+end
diff --git a/lib/webpacker/source.rb b/lib/webpacker/source.rb
new file mode 100644
index 000000000..3c3ca6e13
--- /dev/null
+++ b/lib/webpacker/source.rb
@@ -0,0 +1,28 @@
+class Webpacker::Source
+  def initialize(name)
+    @name = name
+  end
+
+  def path
+    if digesting?
+      "/packs/#{digested_filename}"
+    else
+      "/packs/#{filename}"
+    end
+  end
+
+  private
+    attr_accessor :name
+
+    def digesting?
+      Rails.configuration.x.webpacker[:digesting]
+    end  
+
+    def digested_filename
+      Webpacker::Digests.lookup(name)
+    end
+
+    def filename
+      "#{name}.js"
+    end
+end
diff --git a/webpacker.gemspec b/webpacker.gemspec
new file mode 100644
index 000000000..e62a5eb04
--- /dev/null
+++ b/webpacker.gemspec
@@ -0,0 +1,17 @@
+Gem::Specification.new do |s|
+  s.name     = 'webpacker'
+  s.version  = '0.1'
+  s.authors  = 'David Heinemeier Hansson'
+  s.email    = 'david@basecamp.com'
+  s.summary  = 'Use Webpack to manage app-like JavaScript modules in Rails'
+  s.homepage = 'https://github.com/rails/webpacker'
+  s.license  = 'MIT'
+
+  s.required_ruby_version = '>= 1.9.3'
+
+  s.add_dependency 'activesupport', '>= 3.0.0', '< 5.1'
+  s.add_dependency 'multi_json',    '~> 1.2'
+
+  s.files         = `git ls-files`.split("\n")
+  s.test_files    = `git ls-files -- test/*`.split("\n")
+end