diff --git a/lib/vagrant/config.rb b/lib/vagrant/config.rb
index d77fa22eb..a6aef45aa 100644
--- a/lib/vagrant/config.rb
+++ b/lib/vagrant/config.rb
@@ -1,15 +1,31 @@
+require "vagrant/registry"
+
 module Vagrant
   module Config
     autoload :Base,          'vagrant/config/base'
     autoload :Container,     'vagrant/config/container'
     autoload :ErrorRecorder, 'vagrant/config/error_recorder'
     autoload :Loader,        'vagrant/config/loader'
-    autoload :Top,           'vagrant/config/top'
+    autoload :VersionBase,   'vagrant/config/version_base'
 
     autoload :V1,            'vagrant/config/v1'
 
+    # This is a mutex used to guarantee that only one thread can load
+    # procs at any given time.
     CONFIGURE_MUTEX = Mutex.new
 
+    # This is the registry which keeps track of what configuration
+    # versions are available, mapped by the version string used in
+    # `Vagrant.configure` calls.
+    VERSIONS = Registry.new
+    VERSIONS.register("1") { V1 }
+
+    # This is the order of versions. This is used by the loader to figure out
+    # how to "upgrade" versions up to the desired (current) version. The
+    # current version is always considered to be the last version in this
+    # list.
+    VERSIONS_ORDER = ["1"]
+
     # This is the method which is called by all Vagrantfiles to configure Vagrant.
     # This method expects a block which accepts a single argument representing
     # an instance of the {Config::Top} class.
diff --git a/lib/vagrant/config/loader.rb b/lib/vagrant/config/loader.rb
index 0891e30aa..e2df7ef04 100644
--- a/lib/vagrant/config/loader.rb
+++ b/lib/vagrant/config/loader.rb
@@ -70,8 +70,12 @@ module Vagrant
           @logger.error("Unknown config sources: #{unknown_sources.inspect}")
         end
 
+        # Get the current version config class to use
+        current_version = Config::VERSIONS_ORDER.last
+        current_config_klass = Config::VERSIONS.get(current_version)
+
         # This will hold our result
-        result = V1.init
+        result = current_config_klass.init
 
         @load_order.each do |key|
           next if !@sources.has_key?(key)
@@ -79,14 +83,14 @@ module Vagrant
           @sources[key].each do |proc|
             if !@config_cache.has_key?(proc)
               @logger.debug("Loading from: #{key} (evaluating)")
-              current = V1.load(proc)
+              current = current_config_klass.load(proc)
               @config_cache[proc] = current
             else
               @logger.debug("Loading from: #{key} (cache)")
             end
 
             # Merge the configurations
-            result = V1.merge(result, @config_cache[proc])
+            result = current_config_klass.merge(result, @config_cache[proc])
           end
         end
 
diff --git a/lib/vagrant/config/v1.rb b/lib/vagrant/config/v1.rb
index 71bcf7d51..68616835e 100644
--- a/lib/vagrant/config/v1.rb
+++ b/lib/vagrant/config/v1.rb
@@ -1,10 +1,11 @@
+require "vagrant/config/version_base"
 require "vagrant/config/v1/base"
 require "vagrant/config/v1/root"
 
 module Vagrant
   module Config
     # This is the "version 1" configuration loader.
-    class V1
+    class V1 < VersionBase
       # Returns a bare empty configuration object.
       #
       # @return [V1::Root]
diff --git a/lib/vagrant/config/v1/base.rb b/lib/vagrant/config/v1/base.rb
index 228e4223f..0a05459df 100644
--- a/lib/vagrant/config/v1/base.rb
+++ b/lib/vagrant/config/v1/base.rb
@@ -1,6 +1,6 @@
 module Vagrant
   module Config
-    class V1
+    class V1 < VersionBase
       # Base class for configuration keys. It is not required to inherit
       # from this class but this class provides useful helpers that config
       # classes may wish to use.
diff --git a/lib/vagrant/config/v1/root.rb b/lib/vagrant/config/v1/root.rb
index 809851951..26038e2d6 100644
--- a/lib/vagrant/config/v1/root.rb
+++ b/lib/vagrant/config/v1/root.rb
@@ -1,6 +1,6 @@
 module Vagrant
   module Config
-    class V1
+    class V1 < VersionBase
       # This is the root configuration class. An instance of this is what
       # is passed into version 1 Vagrant configuration blocks.
       class Root
diff --git a/lib/vagrant/config/version_base.rb b/lib/vagrant/config/version_base.rb
new file mode 100644
index 000000000..647ef8ecf
--- /dev/null
+++ b/lib/vagrant/config/version_base.rb
@@ -0,0 +1,45 @@
+module Vagrant
+  module Config
+    # This is the base class for any configuration versions, and includes
+    # the stub methods that configuaration versions must implement. Vagrant
+    # supports configuration versioning so that backwards compatibility can be
+    # maintained for past Vagrantfiles while newer configurations are added.
+    # Vagrant only introduces new configuration versions for major versions
+    # of Vagrant.
+    class VersionBase
+      # Returns an empty configuration object. This can be any kind of object,
+      # since it is treated as an opaque value on the other side, used only
+      # for things like calling into {merge}.
+      #
+      # @return [Object]
+      def self.init
+        raise NotImplementedError
+      end
+
+      # Loads the configuration for the given proc and returns a configuration
+      # object. The return value is treated as an opaque object, so it can be
+      # anything you'd like. The return value is the object that is passed
+      # into methods like {merge}, so it should be something you expect.
+      #
+      # @param [Proc] proc The proc that is to be configured.
+      # @return [Object]
+      def self.load(proc)
+        raise NotImplementedError
+      end
+
+      # Merges two configuration objects, returning the merged object.
+      # The values of `old` and `new` are the opaque objects returned by
+      # {load} or {init}.
+      #
+      # Once again, the return object is treated as an opaque value by
+      # the Vagrant configuration loader, so it can be anything you'd like.
+      #
+      # @param [Object] old Old configuration object.
+      # @param [Object] new New configuration object.
+      # @return [Object] The merged configuration object.
+      def self.merge(old, new)
+        raise NotImplementedError
+      end
+    end
+  end
+end