diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9f4e8962..df41d316 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,7 @@
 master
 ===
 
+* Add support for `environments` with the `-e` CLI flag. Loads additional config from `environments/envname.rb`. Removed `development?` helper in favor of `environment?(:development)`. Added `server?` helper to differentiate between build and server mode.
 * Removed `with_layout`. Use loops of `page` instead.
 * Removed Queryable Sitemap API
 * Removed `css_compressor` setting, use `activate :minify_css, :compressor =>` instead.
diff --git a/middleman-cli/lib/middleman-cli/build.rb b/middleman-cli/lib/middleman-cli/build.rb
index 7b105629..60538431 100644
--- a/middleman-cli/lib/middleman-cli/build.rb
+++ b/middleman-cli/lib/middleman-cli/build.rb
@@ -18,6 +18,10 @@ module Middleman::Cli
     namespace :build
 
     desc 'build [options]', 'Builds the static site for deployment'
+    method_option :environment,
+                  aliases: '-e',
+                  default: ENV['MM_ENV'] || ENV['RACK_ENV'] || 'development',
+                  desc: 'The environment Middleman will run under'
     method_option :clean,
                   type: :boolean,
                   default: true,
@@ -58,18 +62,26 @@ module Middleman::Cli
       @debugging = Middleman::Cli::Base.respond_to?(:debugging) && Middleman::Cli::Base.debugging
       self.had_errors = false
 
-      self.class.shared_instance(options['verbose'], options['instrument'])
+      env = options['environment'].to_sym
+      verbose = options['verbose'] ? 0 : 1
+      instrument = options['instrument']
+
+      app = ::Middleman::Application.server.inst do
+        config[:mode] = :build
+        config[:environment] = env
+        ::Middleman::Logger.singleton(verbose, instrument)
+      end
 
       opts = {}
       opts[:glob]  = options['glob'] if options.key?('glob')
       opts[:clean] = options['clean']
 
-      self.class.shared_instance.run_hook :before_build, self
+      app.run_hook :before_build, self
 
-      action BuildAction.new(self, opts)
+      action BuildAction.new(self, app, opts)
 
-      self.class.shared_instance.run_hook :after_build, self
-      self.class.shared_instance.config_context.execute_after_build_callbacks(self)
+      app.run_hook :after_build, self
+      app.config_context.execute_after_build_callbacks(self)
 
       if had_errors && !debugging
         msg = 'There were errors during this build'
@@ -87,16 +99,6 @@ module Middleman::Cli
       def exit_on_failure?
         true
       end
-
-      # Middleman::Application singleton
-      #
-      # @return [Middleman::Application]
-      def shared_instance(verbose=false, instrument=false)
-        @_shared_instance ||= ::Middleman::Application.server.inst do
-          config[:environment] = :build
-          ::Middleman::Logger.singleton(verbose ? 0 : 1, instrument)
-        end
-      end
     end
   end
 
@@ -109,8 +111,8 @@ module Middleman::Cli
     #
     # @param [Middleman::Cli::Build] base
     # @param [Hash] config
-    def initialize(base, config={})
-      @app        = base.class.shared_instance
+    def initialize(base, app, config={})
+      @app        = app
       @source_dir = Pathname(@app.source_dir)
       @build_dir  = Pathname(@app.config[:build_dir])
       @to_clean   = Set.new
diff --git a/middleman-core/features/mount_rack.feature b/middleman-core/features/mount_rack.feature
index ab105021..dcb83146 100644
--- a/middleman-core/features/mount_rack.feature
+++ b/middleman-core/features/mount_rack.feature
@@ -47,9 +47,7 @@ Feature: Support Rack apps mounted using map
         run MySinatra
       end
 
-      configure :build do
-        endpoint "sinatra/index2.html", path: "/sinatra/"
-      end
+      endpoint "sinatra/index2.html", path: "/sinatra/"
 
       endpoint "dedoo.html", path: "/sinatra/derp.html"
 
diff --git a/middleman-core/fixtures/env-app/config.rb b/middleman-core/fixtures/env-app/config.rb
new file mode 100644
index 00000000..e69de29b
diff --git a/middleman-core/fixtures/env-app/environments/development.rb b/middleman-core/fixtures/env-app/environments/development.rb
new file mode 100644
index 00000000..bce85faf
--- /dev/null
+++ b/middleman-core/fixtures/env-app/environments/development.rb
@@ -0,0 +1 @@
+set :api_key, "dev1"
diff --git a/middleman-core/fixtures/env-app/environments/production.rb b/middleman-core/fixtures/env-app/environments/production.rb
new file mode 100644
index 00000000..1f217266
--- /dev/null
+++ b/middleman-core/fixtures/env-app/environments/production.rb
@@ -0,0 +1,2 @@
+set :api_key, "prod2"
+activate :minify_css
diff --git a/middleman-core/fixtures/env-app/source/index.html.erb b/middleman-core/fixtures/env-app/source/index.html.erb
new file mode 100644
index 00000000..4b6d6950
--- /dev/null
+++ b/middleman-core/fixtures/env-app/source/index.html.erb
@@ -0,0 +1,3 @@
+<script>
+  // load: <%= config[:api_key] %>
+</script>
diff --git a/middleman-core/fixtures/env-app/source/stylesheets/site.css.scss b/middleman-core/fixtures/env-app/source/stylesheets/site.css.scss
new file mode 100644
index 00000000..bcb115c5
--- /dev/null
+++ b/middleman-core/fixtures/env-app/source/stylesheets/site.css.scss
@@ -0,0 +1,3 @@
+body {
+  backgroud: red;
+}
diff --git a/middleman-core/fixtures/generator-test/config.rb b/middleman-core/fixtures/generator-test/config.rb
index 9fc9561c..f3b6a505 100644
--- a/middleman-core/fixtures/generator-test/config.rb
+++ b/middleman-core/fixtures/generator-test/config.rb
@@ -51,8 +51,8 @@
 # Change the images directory
 # set :images_dir, "alternative_image_directory"
 
-# Build-specific configuration
-configure :build do
+# Production build configuration
+configure :production do
   # For example, change the Compass output style for deployment
   # activate :minify_css
 
diff --git a/middleman-core/lib/middleman-core/application.rb b/middleman-core/lib/middleman-core/application.rb
index 64ce952e..e264ea09 100644
--- a/middleman-core/lib/middleman-core/application.rb
+++ b/middleman-core/lib/middleman-core/application.rb
@@ -31,9 +31,6 @@ require 'middleman-core/core_extensions/request'
 # Custom Extension API and config.rb handling
 require 'middleman-core/core_extensions/extensions'
 
-# Catch and show exceptions at the Rack level
-require 'middleman-core/core_extensions/show_exceptions'
-
 # Core Middleman Class
 module Middleman
   class Application
@@ -73,9 +70,13 @@ module Middleman
     # @return [String]
     config.define_setting :source,      'source', 'Name of the source directory'
 
-    # Middleman environment. Defaults to :development, set to :build by the build process
+    # Middleman mode. Defaults to :server, set to :build by the build process
     # @return [String]
-    config.define_setting :environment, ((ENV['MM_ENV'] && ENV['MM_ENV'].to_sym) || :development), 'Middleman environment. Defaults to :development, set to :build by the build process'
+    config.define_setting :mode, ((ENV['MM_ENV'] && ENV['MM_ENV'].to_sym) || :server), 'Middleman mode. Defaults to :server'
+
+    # Middleman environment. Defaults to :development
+    # @return [String]
+    config.define_setting :environment, :development, 'Middleman environment. Defaults to :development'
 
     # Which file should be used for directory indexes
     # @return [String]
@@ -139,9 +140,6 @@ module Middleman
     # Basic Rack Request Handling
     include Middleman::CoreExtensions::Request
 
-    # Handle exceptions
-    include Middleman::CoreExtensions::ShowExceptions
-
     # Setup custom rendering
     include Middleman::CoreExtensions::Rendering
 
@@ -179,9 +177,7 @@ module Middleman
       # Setup the default values from calls to set before initialization
       self.class.config.load_settings(self.class.superclass.config.all_settings)
 
-      ::Middleman::Extensions.auto_activate[:before_sitemap].each do |ext_name|
-        activate ext_name
-      end
+      ::Middleman::Extensions.auto_activate(:before_sitemap, self)
 
       # Initialize the Sitemap
       @sitemap = ::Middleman::Sitemap::Store.new(self)
@@ -204,16 +200,22 @@ module Middleman
       @config_context.define_singleton_method(name, &func)
     end
 
-    # Whether we're in development mode
+    # Whether we're in server mode
     # @return [Boolean] If we're in dev mode
-    def development?
-      config[:environment] == :development
+    def server?
+      config[:mode] == :server
     end
 
     # Whether we're in build mode
-    # @return [Boolean] If we're in build mode
+    # @return [Boolean] If we're in dev mode
     def build?
-      config[:environment] == :build
+      config[:mode] == :build
+    end
+
+    # Whether we're in a specific environment
+    # @return [Boolean]
+    def environment?(key)
+      config[:environment] == key
     end
 
     # The full path to the source directory
diff --git a/middleman-core/lib/middleman-core/config_context.rb b/middleman-core/lib/middleman-core/config_context.rb
index ff5ffa76..96f30d1d 100644
--- a/middleman-core/lib/middleman-core/config_context.rb
+++ b/middleman-core/lib/middleman-core/config_context.rb
@@ -8,7 +8,7 @@ module Middleman
     attr_reader :app
 
     # Whitelist methods that can reach out.
-    delegate :config, :logger, :activate, :use, :map, :mime_type, :data, :root, to: :app
+    delegate :config, :logger, :activate, :use, :map, :mime_type, :data, :files, :root, to: :app
 
     def initialize(app, template_context_class)
       @app = app
@@ -34,6 +34,14 @@ module Middleman
       end
     end
 
+    def include_environment(name)
+      path = File.dirname(__FILE__)
+      other_config = File.join(path, name.to_s)
+      if File.exist? other_config
+        instance_eval File.read(other_config), other_config, 1
+      end
+    end
+
     def ready(&block)
       @ready_callbacks << block
     end
diff --git a/middleman-core/lib/middleman-core/core_extensions.rb b/middleman-core/lib/middleman-core/core_extensions.rb
index 9fd5f985..e85afac3 100644
--- a/middleman-core/lib/middleman-core/core_extensions.rb
+++ b/middleman-core/lib/middleman-core/core_extensions.rb
@@ -11,6 +11,12 @@ Middleman::Extensions.register :data, auto_activate: :before_sitemap do
   Middleman::CoreExtensions::Data
 end
 
+# Catch and show exceptions at the Rack level
+Middleman::Extensions.register :show_exceptions, auto_activate: :before_configuration, modes: [:server] do
+  require 'middleman-core/core_extensions/show_exceptions'
+  Middleman::CoreExtensions::ShowExceptions
+end
+
 # File Change Notifier
 Middleman::Extensions.register :file_watcher, auto_activate: :before_sitemap do
   require 'middleman-core/core_extensions/file_watcher'
diff --git a/middleman-core/lib/middleman-core/core_extensions/extensions.rb b/middleman-core/lib/middleman-core/core_extensions/extensions.rb
index 475024a1..7a76776c 100644
--- a/middleman-core/lib/middleman-core/core_extensions/extensions.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/extensions.rb
@@ -11,8 +11,6 @@ module Middleman
         app.define_hook :instance_available
         app.define_hook :after_configuration
         app.define_hook :before_configuration
-        app.define_hook :build_config
-        app.define_hook :development_config
 
         app.config.define_setting :autoload_sprockets, true, 'Automatically load sprockets at startup?'
         app.config[:autoload_sprockets] = (ENV['AUTOLOAD_SPROCKETS'] == 'true') if ENV['AUTOLOAD_SPROCKETS']
@@ -26,11 +24,11 @@ module Middleman
         #
         # @example
         #    # Only minify when building
-        #    configure :build do
+        #    configure :production do
         #      activate :minify_javascript
         #    end
         #
-        # @param [String, Symbol] env The environment to run in (:build, :development)
+        # @param [String, Symbol] env The environment to run in
         # @return [void]
         def configure(env, &block)
           send("#{env}_config", &block)
@@ -80,18 +78,19 @@ module Middleman
 
       # Override application initialization to load `config.rb` and to call lifecycle hooks.
       def initialize(&block)
-        super
-
         self.class.inst = self
 
         # Search the root of the project for required files
         $LOAD_PATH.unshift(root) unless $LOAD_PATH.include?(root)
 
+        # Evaluate a passed block if given
+        config_context.instance_exec(&block) if block_given?
+
+        super
+
         ::Middleman::Extension.clear_after_extension_callbacks
 
-        ::Middleman::Extensions.auto_activate[:before_configuration].each do |ext_name|
-          activate ext_name
-        end
+        ::Middleman::Extensions.auto_activate(:before_configuration, self)
 
         if config[:autoload_sprockets]
           begin
@@ -102,9 +101,6 @@ module Middleman
           end
         end
 
-        # Evaluate a passed block if given
-        config_context.instance_exec(&block) if block_given?
-
         run_hook :initialized
 
         run_hook :before_configuration
@@ -112,19 +108,17 @@ module Middleman
         # Check for and evaluate local configuration in `config.rb`
         local_config = File.join(root, 'config.rb')
         if File.exist? local_config
-          logger.debug '== Reading:  Local config'
+          logger.debug '== Reading: Local config'
           config_context.instance_eval File.read(local_config), local_config, 1
         end
 
-        if build?
-          run_hook :build_config
-          config_context.execute_configure_callbacks(:build)
+        env_config = File.join(root, 'environments', "#{config[:environment]}.rb")
+        if File.exist? env_config
+          logger.debug "== Reading: #{config[:environment]} config"
+          config_context.instance_eval File.read(env_config), env_config, 1
         end
 
-        if development?
-          run_hook :development_config
-          config_context.execute_configure_callbacks(:development)
-        end
+        config_context.execute_configure_callbacks(config[:environment])
 
         run_hook :instance_available
 
diff --git a/middleman-core/lib/middleman-core/core_extensions/i18n.rb b/middleman-core/lib/middleman-core/core_extensions/i18n.rb
index e83f7cfc..41e2ba0f 100644
--- a/middleman-core/lib/middleman-core/core_extensions/i18n.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/i18n.rb
@@ -37,9 +37,7 @@ class Middleman::CoreExtensions::Internationalization < ::Middleman::Extension
 
     configure_i18n
 
-    unless app.build?
-      logger.info "== Locales: #{langs.join(', ')} (Default #{@mount_at_root})"
-    end
+    logger.info "== Locales: #{langs.join(', ')} (Default #{@mount_at_root})"
 
     # Don't output localizable files
     app.ignore File.join(options[:templates_dir], '**')
diff --git a/middleman-core/lib/middleman-core/core_extensions/show_exceptions.rb b/middleman-core/lib/middleman-core/core_extensions/show_exceptions.rb
index 67fad3c3..3f039ca6 100644
--- a/middleman-core/lib/middleman-core/core_extensions/show_exceptions.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/show_exceptions.rb
@@ -1,21 +1,14 @@
 # Support rack/showexceptions during development
-module Middleman
-  module CoreExtensions
-    module ShowExceptions
-      def self.included(app)
-        # Require lib
-        require 'rack/showexceptions'
+module Middleman::CoreExtensions
+  class ShowExceptions < ::Middleman::Extension
+    def initialize(app, options_hash={}, &block)
+      super
 
-        # Whether to catch and display exceptions
-        # @return [Boolean]
-        app.config.define_setting :show_exceptions, true, 'Whether to catch and display exceptions'
+      require 'rack/showexceptions'
+    end
 
-        # When in dev
-        app.configure :development do
-          # Include middlemare
-          use ::Rack::ShowExceptions if config[:show_exceptions]
-        end
-      end
+    def after_configuration
+      app.use ::Rack::ShowExceptions
     end
   end
 end
diff --git a/middleman-core/lib/middleman-core/extensions.rb b/middleman-core/lib/middleman-core/extensions.rb
index 519493be..a33bf203 100644
--- a/middleman-core/lib/middleman-core/extensions.rb
+++ b/middleman-core/lib/middleman-core/extensions.rb
@@ -14,6 +14,8 @@ module Middleman
       before_configuration: []
     }
 
+    AutoActivation = Struct.new(:name, :modes)
+
     class << self
       # @api private
       # A hash of all registered extensions. Registered extensions are not necessarily active - this
@@ -21,12 +23,6 @@ module Middleman
       # @return [Hash{Symbol => Class<Middleman::Extension>, Proc}] A directory of known extensions indexed by the name they were registered under. The value may be a Proc, which can be lazily called to return an extension class.
       attr_reader :registered
 
-      # @api private
-      # A list of extensions that should be automatically loaded at different points in the application startup lifecycle.
-      # Only internal, built-in Middleman extensions should be listed here.
-      # @return [Hash{Symbol => Symbol}] A hash from event name to extension name.
-      attr_reader :auto_activate
-
       # Register a new extension. Choose a name which will be
       # used to activate the extension in `config.rb`, like this:
       #
@@ -71,7 +67,10 @@ module Middleman
           raise 'You must provide a Middleman::Extension or a block that returns a Middleman::Extension'
         end
 
-        @auto_activate[options[:auto_activate]] << name if options[:auto_activate]
+        if options[:auto_activate]
+          descriptor = AutoActivation.new(name, options[:modes] || :all)
+          @auto_activate[options[:auto_activate]] << descriptor
+        end
       end
 
       # @api private
@@ -106,7 +105,19 @@ module Middleman
       # A flattened list of all extensions which are automatically activated
       # @return [Array<Symbol>] A list of extension names which are automatically activated.
       def auto_activated
-        @auto_activate.values.flatten
+        @auto_activate.values.map(&:name).flatten
+      end
+
+      # @api private
+      # Load autoactivatable extensions for the given env.
+      # @param [Symbol] group The name of the auto_activation group.
+      # @param [Middleman::Application] app An instance of the app.
+      def auto_activate(group, app)
+        @auto_activate[group].each do |descriptor|
+          if descriptor[:modes] == :all || descriptor[:modes].include?(app.config[:mode])
+            app.activate descriptor[:name]
+          end
+        end
       end
     end
   end
diff --git a/middleman-core/lib/middleman-core/renderers/coffee_script.rb b/middleman-core/lib/middleman-core/renderers/coffee_script.rb
index e6f57cb4..b8519845 100644
--- a/middleman-core/lib/middleman-core/renderers/coffee_script.rb
+++ b/middleman-core/lib/middleman-core/renderers/coffee_script.rb
@@ -30,7 +30,7 @@ module Middleman
         # @param [Hash] locals
         # @return [String]
         def evaluate(context, locals, &block)
-          return super if middleman_app.build?
+          return super unless middleman_app.server?
 
           begin
             super
diff --git a/middleman-core/lib/middleman-core/step_definitions/server_steps.rb b/middleman-core/lib/middleman-core/step_definitions/server_steps.rb
index c72d8712..4ea87dc8 100644
--- a/middleman-core/lib/middleman-core/step_definitions/server_steps.rb
+++ b/middleman-core/lib/middleman-core/step_definitions/server_steps.rb
@@ -29,10 +29,6 @@ Given /^"([^\"]*)" is set to "([^\"]*)"$/ do |variable, value|
   }
 end
 
-Given /^current environment is "([^\"]*)"$/ do |env|
-  @current_env = env.to_sym
-end
-
 Given /^the Server is running$/ do
   root_dir = File.expand_path(current_dir)
 
@@ -45,14 +41,12 @@ Given /^the Server is running$/ do
   ENV['MM_ROOT'] = root_dir
 
   initialize_commands = @initialize_commands || []
-  initialize_commands.unshift lambda {
-    config[:environment] = @current_env || :development
-    config[:show_exceptions] = false
-  }
 
   @server_inst = Middleman::Application.server.inst do
-    initialize_commands.each do |p|
-      instance_exec(&p)
+    app.initialized do
+      initialize_commands.each do |p|
+        config_context.instance_exec(&p)
+      end
     end
   end
 
diff --git a/middleman-core/lib/middleman-core/template_context.rb b/middleman-core/lib/middleman-core/template_context.rb
index 48ccad41..a81db78b 100644
--- a/middleman-core/lib/middleman-core/template_context.rb
+++ b/middleman-core/lib/middleman-core/template_context.rb
@@ -19,7 +19,7 @@ module Middleman
     attr_accessor :current_engine
 
     # Shorthand references to global values on the app instance.
-    delegate :config, :logger, :sitemap, :build?, :development?, :data, :extensions, :source_dir, :root, to: :app
+    delegate :config, :logger, :sitemap, :server?, :build?, :environment?, :data, :extensions, :source_dir, :root, to: :app
 
     # Initialize a context with the current app and predefined locals and options hashes.
     #