diff --git a/middleman-core/lib/middleman-core/application.rb b/middleman-core/lib/middleman-core/application.rb
index be560400..b65c05fe 100644
--- a/middleman-core/lib/middleman-core/application.rb
+++ b/middleman-core/lib/middleman-core/application.rb
@@ -12,10 +12,14 @@ require "middleman-core/vendor/hooks-0.2.0/lib/hooks"
 require "middleman-core/sitemap"
 
 require "middleman-core/core_extensions"
+require "middleman-core/configuration"
 
 # Core Middleman Class
 module Middleman
   class Application
+    # Global configuration
+    include Configuration::Global
+
     # Uses callbacks
     include Hooks
 
@@ -34,50 +38,19 @@ module Middleman
         class_eval(&block)   if block_given?
         include(*extensions) if extensions.any?
       end
-
-      # Access class-wide defaults
-      #
-      # @private
-      # @return [Hash] Hash of default values
-      def defaults
-        @defaults ||= {}
-      end
-
-      # Set class-wide defaults
-      #
-      # @param [Symbol] key Unique key name
-      # @param value Default value
-      # @return [void]
-      def set(key, value=nil, &block)
-        @defaults ||= {}
-        @defaults[key] = value
-
-        @inst.set(key, value, &block) if @inst
-      end
     end
 
     delegate :helpers, :to => :"self.class"
 
-    # Set attributes (global variables)
-    #
-    # @param [Symbol] key Name of the attribue
-    # @param value Attribute value
-    # @return [void]
-    def set(key, value=nil, &block)
-      setter = "#{key}=".to_sym
-      self.class.send(:attr_accessor, key) if !respond_to?(setter)
-      value = block if block_given?
-      send(setter, value)
-    end
-
     # Root project directory (overwritten in middleman build/server)
     # @return [String]
     set :root,        ENV["MM_ROOT"] || Dir.pwd
 
     # Pathname-addressed root
-    def root_path
-      @_root_path ||= Pathname.new(root)
+    def self.root_path
+      Pathname(root)
     end
+    delegate :root_path, :to => :"self.class"
 
     # Name of the source directory
     # @return [String]
@@ -178,7 +151,7 @@ module Middleman
       cache.clear
 
       # Setup the default values from calls to set before initialization
-      self.class.superclass.defaults.each { |k,v| set(k,v) }
+      self.class.superclass.config.to_h.each { |k,v| self.class.set(k,v) }
 
       # Evaluate a passed block if given
       instance_exec(&block) if block_given?
@@ -205,13 +178,6 @@ module Middleman
     # @return [Boolean] If we're in build mode
     def build?; environment == :build; end
 
-    # Backwards compatibilty with old Sinatra template interface
-    #
-    # @return [Middleman::Application]
-    def settings
-      self
-    end
-
     # The full path to the source directory
     #
     # @return [String]
diff --git a/middleman-core/lib/middleman-core/configuration.rb b/middleman-core/lib/middleman-core/configuration.rb
new file mode 100644
index 00000000..4ee8211a
--- /dev/null
+++ b/middleman-core/lib/middleman-core/configuration.rb
@@ -0,0 +1,218 @@
+module Middleman
+  module Configuration
+    # Access to a global configuration manager for the whole Middleman project, 
+    # plus backwards compatibility mechanisms for older Middleman projects.
+    module Global
+      def self.included(app)
+        app.send :extend, ClassMethods
+      end
+
+      module ClassMethods
+        # Global configuration for the whole Middleman project.
+        # @return [ConfigurationManager]
+        def config
+          @_config ||= ConfigurationManager.new
+        end
+
+        # Set attributes (global variables)
+        #
+        # @deprecated Prefer accessing settings through "config".
+        #
+        # @param [Symbol] key Name of the attribue
+        # @param value Attribute value
+        # @return [void]
+        def set(key, default=nil, &block)
+          config.define_setting(key, default)
+          @inst.set(key, default, &block) if @inst
+        end
+
+        # Access global settings as methods, to preserve compatibility with
+        # old Middleman.
+        #
+        # @deprecated Prefer accessing settings through "config".
+        def method_missing(method)
+          if config.defines_setting? method
+            config[method]
+          else
+            super
+          end
+        end
+
+        # Needed so that method_missing makes sense
+        def respond_to?(method, include_private = false)
+          super || config.defines_setting?(method)
+        end
+      end
+
+      def config
+        self.class.config
+      end
+
+      # Backwards compatibilty with old Sinatra template interface
+      #
+      # @deprecated Prefer accessing settings through "config".
+      #
+      # @return [ConfigurationManager]
+      alias :settings :config
+
+      # Set attributes (global variables)
+      #
+      # @deprecated Prefer accessing settings through "config".
+      #
+      # @param [Symbol] key Name of the attribue
+      # @param value Attribute value
+      # @return [void]
+      def set(key, value=nil, &block)
+        value = block if block_given?
+        config[key] = value
+      end
+
+      # Access global settings as methods, to preserve compatibility with
+      # old Middleman.
+      #
+      # @deprecated Prefer accessing settings through "config".
+      def method_missing(method)
+        if config.defines_setting? method
+          config[method]
+        else
+          super
+        end
+      end
+
+      # Needed so that method_missing makes sense
+      def respond_to?(method, include_private = false)
+        super || config.defines_setting?(method)
+      end
+    end
+
+    # A class that manages a collection of documented settings.
+    # Can be used by extensions as well as the main Middleman
+    # application. Extensions should probably finalize their instance
+    # after defining all the settings they want to expose.
+    class ConfigurationManager
+      def initialize
+        # A hash from setting key to ConfigSetting instance.
+        @settings = {}
+        @finalized = false
+      end
+
+      # Get all settings, sorted by key, as ConfigSetting objects.
+      # @return [Array<ConfigSetting>]
+      def all_settings
+        @settings.values.sort_by(&:key)
+      end
+
+      # Get a full ConfigSetting object for the setting with the give key.
+      # @return [ConfigSetting]
+      def setting(key)
+        @settings[key]
+      end
+
+      # Get the value of a setting by key. Returns nil if there is no such setting.
+      # @return [Object]
+      def [](key)
+        setting = @settings[key]
+        setting ? setting.value : nil
+      end
+
+      # Set the value of a setting by key. Creates the setting if it doesn't exist.
+      # @param [Symbol] key
+      # @param [Object] val
+      def []=(key, val)
+        setting = @settings[key] || define_setting(key)
+        setting.value = val
+      end
+
+      # Allow configuration settings to be read and written via methods
+      def method_missing(method, *args)
+        if defines_setting?(method) && args.size == 0
+          self[method]
+        elsif method =~ /^(\w+)=$/ && args.size == 1
+          self[$1] = args[0]
+        else
+          super
+        end
+      end
+
+      # Needed so that method_missing makes sense
+      def respond_to?(method, include_private = false)
+        super || defines_setting?(method) || (method =~ /^(\w+)=$/ && defines_setting?($1))
+      end
+
+      # Does this configuration manager know about the setting identified by key?
+      # @param [Symbol] key
+      # @return [Boolean]
+      def defines_setting?(key)
+        @settings.has_key?(key)
+      end
+
+      # Define a new setting, with optional default and user-friendly description.
+      # Once the configuration manager is finalized, no new settings may be defined.
+      #
+      # @param [Symbol] key
+      # @param [Object] default
+      # @param [String] description
+      # @return [ConfigSetting]
+      def define_setting(key, default=nil, description=nil)
+        raise "Setting #{key} doesn't exist" if @finalized
+        raise "Setting #{key} already defined" if @settings.has_key?(key)
+        raise "Setting key must be a Symbol" unless key.is_a? Symbol
+
+        @settings[key] = ConfigSetting.new(key, default, description)
+      end
+
+      # Switch the configuration manager is finalized, it switches to read-only
+      # mode and no new settings may be defined.
+      def finalize!
+        @finalized = true
+      end
+
+      # Deep duplicate of the configuration manager
+      def dup
+        copy = ConfigurationManager.new
+        @settings.each do |key, setting|
+          copy_setting = copy.define_setting setting.key, setting.default, setting.description
+          copy_setting.value = setting.value if setting.value_set?
+        end
+        copy
+      end
+
+      def to_h
+        hash = {}
+        @settings.each do |key, setting|
+          hash[key] = setting.value
+        end
+        hash
+      end
+
+      def to_s
+        to_h.inspect
+      end
+    end
+
+    class ConfigSetting
+      attr_accessor :key, :default, :description
+      attr_writer :value
+
+      def initialize(key, default, description)
+        @value_set = false
+        self.key = key
+        self.default = default
+        self.description = description
+      end
+
+      def value=(value)
+        @value = value
+        @value_set = true
+      end
+
+      def value
+        value_set? ? @value : default
+      end
+
+      def value_set?
+        @value_set
+      end
+    end
+  end
+end
diff --git a/middleman-core/lib/middleman-core/core_extensions/extensions.rb b/middleman-core/lib/middleman-core/core_extensions/extensions.rb
index e10359ab..9f77b510 100644
--- a/middleman-core/lib/middleman-core/core_extensions/extensions.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/extensions.rb
@@ -37,9 +37,6 @@ module Middleman
       class << self
         # @private
         def registered(app)
-          # Using for version parsing
-          require "rubygems"
-
           app.define_hook :after_configuration
           app.define_hook :before_configuration
           app.define_hook :build_config