diff --git a/lib/vagrant/action/builder.rb b/lib/vagrant/action/builder.rb
index 4be32d2fd..f10d3e58a 100644
--- a/lib/vagrant/action/builder.rb
+++ b/lib/vagrant/action/builder.rb
@@ -1,26 +1,50 @@
 module Vagrant
   class Action
+    # Action builder which provides a nice DSL for building up
+    # a middleware sequence for Vagrant actions. This code is based
+    # heavily off of `Rack::Builder` and `ActionDispatch::MiddlewareStack`
+    # in Rack and Rails, respectively.
     class Builder
+      # Initializes the builder. An optional block can be passed which
+      # will be evaluated in the context of the instance.
       def initialize(&block)
         instance_eval(&block) if block_given?
       end
 
+      # Returns the current stack of middlewares. You probably won't
+      # need to use this directly, and its recommended that you don't.
+      #
+      # @return [Array]
       def stack
         @stack ||= []
       end
 
+      # Adds a middleware class to the middleware stack. Any additional
+      # args and a block, if given, are saved and passed to the initializer
+      # of the middleware.
+      #
+      # @param [Class] middleware The middleware class
       def use(middleware, *args, &block)
         stack << [middleware, args, block]
       end
 
-      def to_app
-        inner = @ins.last
+      # Converts the builder stack to a runnable action sequence.
+      #
+      # @param [Vagrant::Action::Environment] env The action environment
+      # @return [Object] A callable object
+      def to_app(env)
+        items = stack.collect do |item|
+          klass, args, block = item
+          lambda { |app| klass.new(app, env, *args, &block) }
+        end
 
-        @ins[0...-1].reverse.inject(inner) { |a,e| e.call(a) }
+        items << lambda { |env| } # The final step, which simply returns
+        items[0...-1].reverse.inject(items.last) { |a,e| e.call(a) }
       end
 
+      # Runs the builder stack with the given environment.
       def call(env)
-        to_app.call(env)
+        to_app(env).call(env)
       end
     end
   end
diff --git a/lib/vagrant/action/environment.rb b/lib/vagrant/action/environment.rb
new file mode 100644
index 000000000..974ae4483
--- /dev/null
+++ b/lib/vagrant/action/environment.rb
@@ -0,0 +1,17 @@
+module Vagrant
+  class Action
+    # Represents an action environment which is what is passed
+    # to the `call` method of each action. This environment contains
+    # some helper methods for accessing the environment as well
+    # as being a hash, to store any additional options.
+    class Environment < Hash
+      # The {Vagrant::Environment} object represented by this
+      # action environment.
+      attr_reader :env
+
+      def new(env)
+        @env = env
+      end
+    end
+  end
+end
diff --git a/lib/vagrant/actions/middleware_stack.rb b/lib/vagrant/actions/middleware_stack.rb
deleted file mode 100644
index f28bf16b7..000000000
--- a/lib/vagrant/actions/middleware_stack.rb
+++ /dev/null
@@ -1,22 +0,0 @@
-module Vagrant
-  module Actions
-    # Represents a middleware stack for Vagrant actions. Vagrant
-    # actions are created and can be extended with middlewares.
-    #
-    # The exact nature of how this will work is not set in stone.
-    class MiddlewareStack
-      # Initializes the middleware stack with the given name.
-      def initialize(key)
-        @stack = []
-      end
-
-      def use(klass)
-        @stack << klass
-      end
-
-      def run(endpoint)
-        @stack << endpoint
-      end
-    end
-  end
-end
diff --git a/test/vagrant/action/builder_test.rb b/test/vagrant/action/builder_test.rb
index ad6f8d9f3..a0581b20d 100644
--- a/test/vagrant/action/builder_test.rb
+++ b/test/vagrant/action/builder_test.rb
@@ -36,7 +36,41 @@ class ActionBuilderTest < Test::Unit::TestCase
     end
 
     context "converting to an app" do
+      should "initialize each middleware with app and env" do
+        # TODO: better testing of this method... somehow
 
+        result = mock("result")
+        env = {:a => :b}
+        middleware = mock("middleware")
+        middleware.expects(:new).with(anything, env).returns(result)
+        @instance.use middleware
+        assert_equal result, @instance.to_app(env)
+      end
+    end
+
+    context "calling" do
+      def mock_middleware
+        middleware = Class.new do
+          def initialize(app, env)
+            @app = app
+          end
+
+          def call(env)
+            @app.call(env)
+          end
+        end
+      end
+
+      should "convert to an app then call with the env" do
+        mw = mock_middleware
+        mw.any_instance.expects(:call).with() do |env|
+          assert env.has_key?(:key)
+          true
+        end
+
+        @instance.use(mw)
+        @instance.call(:key => :value)
+      end
     end
   end
 end
diff --git a/test/vagrant/action/environment_test.rb b/test/vagrant/action/environment_test.rb
new file mode 100644
index 000000000..1d9ef3d2d
--- /dev/null
+++ b/test/vagrant/action/environment_test.rb
@@ -0,0 +1,8 @@
+require File.join(File.dirname(__FILE__), '..', '..', 'test_helper')
+
+class ActionEnvironmentTest < Test::Unit::TestCase
+  setup do
+    @klass = Vagrant::Action::Environment
+  end
+
+end