diff --git a/guides/source/configuring.textile b/guides/source/configuring.textile
index 2c90143394..27eaf1cbc5 100644
--- a/guides/source/configuring.textile
+++ b/guides/source/configuring.textile
@@ -87,6 +87,10 @@ end
 
 * +config.dependency_loading+ is a flag that allows you to disable constant autoloading setting it to false. It only has effect if +config.cache_classes+ is true, which it is by default in production mode. This flag is set to false by +config.threadsafe!+.
 
+* +config.eager_load+ when true, eager loads all registered `config.eager_load_namespaces`. This includes your application, engines, Rails frameworks and any other registered namespace.
+
+* +config.eager_load_namespaces+ registers namespaces that are eager loaded when +config.eager_load+ is true. All namespaces in the list must respond to the +eager_load!+ method.
+
 * +config.eager_load_paths+ accepts an array of paths from which Rails will eager load on boot if cache classes is enabled. Defaults to every folder in the +app+ directory of the application.
 
 * +config.encoding+ sets up the application-wide encoding. Defaults to UTF-8.
@@ -125,10 +129,6 @@ config.session_store :my_custom_store
 
 This custom store must be defined as +ActionDispatch::Session::MyCustomStore+. In addition to symbols, they can also be objects implementing a certain API, like +ActiveRecord::SessionStore+, in which case no special namespace is required.
 
-* +config.threadsafe!+ enables +cache_classes+ and +eager_load+ to make the application threadsafe.
-
-WARNING: Threadsafe operation is incompatible with the normal workings of development mode Rails. In particular, automatic dependency loading and class reloading are automatically disabled when you call +config.threadsafe!+.
-
 * +config.time_zone+ sets the default time zone for the application and enables time zone awareness for Active Record.
 
 * +config.whiny_nils+ enables or disables warnings when a certain set of methods are invoked on +nil+ and it does not respond to them. Defaults to true in development and test environments.
@@ -746,13 +746,13 @@ The error occurred while evaluating nil.each
 
 *+build_middleware_stack+* Builds the middleware stack for the application, returning an object which has a +call+ method which takes a Rack environment object for the request.
 
-*+eager_load!+* If +config.cache_classes+ is true, runs the +config.before_eager_load+ hooks and then calls +eager_load!+ which will load all the Ruby files from +config.eager_load_paths+.
+*+eager_load!+* If +config.eager_load+ is true, runs the +config.before_eager_load+ hooks and then calls +eager_load!+ which will load all +config.eager_load_namespaces+.
 
 *+finisher_hook+* Provides a hook for after the initialization of process of the application is complete, as well as running all the +config.after_initialize+ blocks for the application, railties and engines.
 
 *+set_routes_reloader+* Configures Action Dispatch to reload the routes file using +ActionDispatch::Callbacks.to_prepare+.
 
-*+disable_dependency_loading+* Disables the automatic dependency loading if the +config.cache_classes+ is set to true and +config.dependency_loading+ is set to false.
+*+disable_dependency_loading+* Disables the automatic dependency loading if the +config.eager_load+ is set to true.
 
 h3. Database pooling
 
diff --git a/railties/CHANGELOG.md b/railties/CHANGELOG.md
index 851f41249a..fea18b5f47 100644
--- a/railties/CHANGELOG.md
+++ b/railties/CHANGELOG.md
@@ -5,6 +5,8 @@
     default_url_options[:script_name] to set proper application's mount point by
     yourself. *Piotr Sarnacki*
 
+*   `config.threadsafe!` is deprecated in favor of `config.eager_load` which provides a more fine grained control on what is eager loaded *José Valim*
+
 *   The migration generator will now produce AddXXXToYYY/RemoveXXXFromYYY migrations with references statements, for instance
 
         rails g migration AddReferencesToProducts user:references supplier:references{polymorphic}
diff --git a/railties/lib/rails/application/configuration.rb b/railties/lib/rails/application/configuration.rb
index 5c7cf412ac..7f05b2e7e1 100644
--- a/railties/lib/rails/application/configuration.rb
+++ b/railties/lib/rails/application/configuration.rb
@@ -90,11 +90,10 @@ module Rails
         end
       end
 
-      # Enable threaded mode. Allows concurrent requests to controller actions and
-      # multiple database connections. Also disables automatic dependency loading
-      # after boot, and disables reloading code on every request, as these are
-      # fundamentally incompatible with thread safety.
       def threadsafe!
+        ActiveSupport::Deprecation.warn "config.threadsafe! is deprecated. Rails applications " \
+          "behave by default as thread safe in production as long as config.cache_classes and " \
+          "config.eager_load are set to true"
         @cache_classes = true
         @eager_load = true
         self
diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index 26f8aad95b..ebdbbaee8b 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -139,34 +139,31 @@ module ApplicationTests
       assert_instance_of Pathname, Rails.root
     end
 
-    test "marking the application as threadsafe sets the correct config variables" do
+    test "initialize an eager loaded, cache classes app" do
       add_to_config <<-RUBY
-        config.threadsafe!
-      RUBY
-
-      require "#{app_path}/config/application"
-      assert AppTemplate::Application.config.cache_classes
-      assert AppTemplate::Application.config.eager_load
-    end
-
-    test "initialize a threadsafe app" do
-      add_to_config <<-RUBY
-        config.threadsafe!
+        config.eager_load = true
+        config.cache_classes = true
       RUBY
 
       require "#{app_path}/config/application"
       assert AppTemplate::Application.initialize!
     end
 
+    test "application is always added to eager_load namespaces" do
+      require "#{app_path}/config/application"
+      assert AppTemplate::Application, AppTemplate::Application.config.eager_load_namespaces
+    end
+
     test "asset_path defaults to nil for application" do
       require "#{app_path}/config/environment"
       assert_equal nil, AppTemplate::Application.config.asset_path
     end
 
-    test "the application can be marked as threadsafe when there are no frameworks" do
+    test "the application can be eager loaded even when there are no frameworks" do
       FileUtils.rm_rf("#{app_path}/config/environments")
       add_to_config <<-RUBY
-        config.threadsafe!
+        config.eager_load = true
+        config.cache_classes = true
       RUBY
 
       use_frameworks []