diff --git a/lib/puppet/interface/interface_collection.rb b/lib/puppet/interface/interface_collection.rb
index 51b7534a0..115892397 100644
--- a/lib/puppet/interface/interface_collection.rb
+++ b/lib/puppet/interface/interface_collection.rb
@@ -1,52 +1,87 @@
 require 'puppet/interface'
 
 module Puppet::Interface::InterfaceCollection
+  SEMVER_VERSION = /^(\d+)\.(\d+)\.(\d+)([A-Za-z][0-9A-Za-z-]*|)$/
+
   @interfaces = Hash.new { |hash, key| hash[key] = {} }
 
   def self.interfaces
     unless @loaded
       @loaded = true
       $LOAD_PATH.each do |dir|
         next unless FileTest.directory?(dir)
         Dir.chdir(dir) do
           Dir.glob("puppet/interface/v*/*.rb").collect { |f| f.sub(/\.rb/, '') }.each do |file|
             iname = file.sub(/\.rb/, '')
             begin
               require iname
             rescue Exception => detail
               puts detail.backtrace if Puppet[:trace]
               raise "Could not load #{iname} from #{dir}/#{file}: #{detail}"
             end
           end
         end
       end
     end
     return @interfaces.keys
   end
 
+  def self.versions(name)
+    versions = []
+    $LOAD_PATH.each do |dir|
+      next unless FileTest.directory?(dir)
+      v_dir = File.join dir, %w[puppet interface v*]
+      Dir.glob(File.join v_dir, "#{name}{.rb,/*.rb}").each do |f|
+        v = f.sub(%r[.*/v([^/]+?)/#{name}(?:(?:/[^/]+)?.rb)$], '\1')
+        if v =~ SEMVER_VERSION
+          versions << v
+        else
+          warn "'#{v}' (#{f}) is not a valid version string; skipping"
+        end
+      end
+    end
+    return versions.uniq.sort { |a, b| compare_versions(a, b)  }
+  end
+
+  def self.compare_versions(a, b)
+    a, b = [a, b].map do |x|
+      parts = SEMVER_VERSION.match(x).to_a[1..4]
+      parts[0..2] = parts[0..2].map { |e| e.to_i }
+      parts
+    end
+
+    cmp = a[0..2] <=> b[0..2]
+    if cmp == 0
+      cmp = a[3] <=> b[3]
+      cmp = +1 if a[3].empty? && !b[3].empty?
+      cmp = -1 if b[3].empty? && !a[3].empty?
+    end
+    cmp
+  end
+
   def self.[](name, version)
     @interfaces[underscorize(name)][version] if interface?(name, version)
   end
 
   def self.interface?(name, version)
     name = underscorize(name)
     unless @interfaces.has_key?(name) && @interfaces[name].has_key?(version)
       require "puppet/interface/v#{version}/#{name}"
     end
     return @interfaces.has_key?(name) && @interfaces[name].has_key?(version)
   rescue LoadError
     return false
   end
 
   def self.register(interface)
     @interfaces[underscorize(interface.name)][interface.version] = interface
   end
 
   def self.underscorize(name)
     unless name.to_s =~ /^[-_a-z]+$/i then
       raise ArgumentError, "#{name.inspect} (#{name.class}) is not a valid interface name"
     end
 
     name.to_s.downcase.split(/[-_]/).join('_').to_sym
   end
 end
diff --git a/spec/unit/interface/interface_collection_spec.rb b/spec/unit/interface/interface_collection_spec.rb
index a404d85a6..a943c2ec2 100644
--- a/spec/unit/interface/interface_collection_spec.rb
+++ b/spec/unit/interface/interface_collection_spec.rb
@@ -1,101 +1,203 @@
 #!/usr/bin/env ruby
 
 require File.expand_path(File.dirname(__FILE__) + '/../../spec_helper.rb')
+require 'tmpdir'
 
 describe Puppet::Interface::InterfaceCollection do
   before :all do
     @interfaces = subject.instance_variable_get("@interfaces").dup
   end
 
   before :each do
     subject.instance_variable_get("@interfaces").clear
   end
 
   after :all do
     subject.instance_variable_set("@interfaces", @interfaces)
   end
 
   describe "::interfaces" do
   end
 
+  describe "::versions" do
+    before :each do
+      @dir = Dir.mktmpdir
+      @lib = FileUtils.mkdir_p(File.join @dir, 'puppet', 'interface')
+      $LOAD_PATH.push(@dir)
+    end
+
+    after :each do
+      FileUtils.remove_entry_secure @dir
+      $LOAD_PATH.pop
+    end
+
+    it "should return an empty array when no versions are loadable" do
+      subject.versions(:fozzie).should == []
+    end
+
+    it "should return versions loadable as puppet/interface/v{version}/{name}" do
+      FileUtils.mkdir_p(File.join @lib, 'v1.0.0')
+      FileUtils.touch(File.join @lib, 'v1.0.0', 'fozzie.rb')
+      subject.versions(:fozzie).should == ['1.0.0']
+    end
+
+    it "should an ordered list of all versions loadable as puppet/interface/v{version}/{name}" do
+      %w[ 1.2.1rc2 1.2.1beta1 1.2.1rc1 1.2.1 1.2.2 ].each do |version|
+        FileUtils.mkdir_p(File.join @lib, "v#{version}")
+        FileUtils.touch(File.join @lib, "v#{version}", 'fozzie.rb')
+      end
+      subject.versions(:fozzie).should == %w[ 1.2.1beta1 1.2.1rc1 1.2.1rc2 1.2.1 1.2.2 ]
+    end
+
+    it "should not return a version for an empty puppet/interface/v{version}/{name}" do
+      FileUtils.mkdir_p(File.join @lib, 'v1.0.0', 'fozzie')
+      subject.versions(:fozzie).should == []
+    end
+
+    it "should an ordered list of all versions loadable as puppet/interface/v{version}/{name}/*.rb" do
+      %w[ 1.2.1rc2 1.2.1beta1 1.2.1rc1 1.2.1 1.2.2 ].each do |version|
+        FileUtils.mkdir_p(File.join @lib, "v#{version}", "fozzie")
+        FileUtils.touch(File.join @lib, "v#{version}", 'fozzie', 'action.rb')
+      end
+      subject.versions(:fozzie).should == %w[ 1.2.1beta1 1.2.1rc1 1.2.1rc2 1.2.1 1.2.2 ]
+    end
+  end
+
+  describe "::compare_versions" do
+    # (a <=> b) should be:
+    #   -1 if a < b
+    #   0  if a == b
+    #   1  if a > b
+    it 'should sort major version numbers numerically' do
+      subject.compare_versions('1.0.0', '2.0.0').should == -1
+      subject.compare_versions('2.0.0', '1.1.1').should == 1
+      subject.compare_versions('2.0.0', '10.0.0').should == -1
+    end
+
+    it 'should sort minor version numbers numerically' do
+      subject.compare_versions('0.1.0', '0.2.0').should == -1
+      subject.compare_versions('0.2.0', '0.1.1').should == 1
+      subject.compare_versions('0.2.0', '0.10.0').should == -1
+    end
+
+    it 'should sort tiny version numbers numerically' do
+      subject.compare_versions('0.0.1', '0.0.2').should == -1
+      subject.compare_versions('0.0.2', '0.0.1').should == 1
+      subject.compare_versions('0.0.2', '0.0.10').should == -1
+    end
+
+    it 'should sort major version before minor version' do
+      subject.compare_versions('1.1.0', '1.2.0').should == -1
+      subject.compare_versions('1.2.0', '1.1.1').should == 1
+      subject.compare_versions('1.2.0', '1.10.0').should == -1
+
+      subject.compare_versions('1.1.0', '2.2.0').should == -1
+      subject.compare_versions('2.2.0', '1.1.1').should == 1
+      subject.compare_versions('2.2.0', '1.10.0').should == 1
+    end
+
+    it 'should sort minor version before tiny version' do
+      subject.compare_versions('0.1.1', '0.1.2').should == -1
+      subject.compare_versions('0.1.2', '0.1.1').should == 1
+      subject.compare_versions('0.1.2', '0.1.10').should == -1
+
+      subject.compare_versions('0.1.1', '0.2.2').should == -1
+      subject.compare_versions('0.2.2', '0.1.1').should == 1
+      subject.compare_versions('0.2.2', '0.1.10').should == 1
+    end
+
+    it 'should sort appended strings asciibetically' do
+      subject.compare_versions('0.0.0a', '0.0.0b').should == -1
+      subject.compare_versions('0.0.0beta1', '0.0.0beta2').should == -1
+      subject.compare_versions('0.0.0beta1', '0.0.0rc1').should == -1
+      subject.compare_versions('0.0.0beta1', '0.0.0alpha1').should == 1
+      subject.compare_versions('0.0.0beta1', '0.0.0beta1').should == 0
+    end
+
+    it "should sort appended strings before 'whole' versions" do
+      subject.compare_versions('0.0.1a', '0.0.1').should == -1
+      subject.compare_versions('0.0.1', '0.0.1beta').should == 1
+    end
+  end
+
   describe "::[]" do
     before :each do
       subject.instance_variable_get("@interfaces")[:foo]['0.0.1'] = 10
     end
 
     it "should return the interface with the given name" do
       subject["foo", '0.0.1'].should == 10
     end
 
     it "should attempt to load the interface if it isn't found" do
       subject.expects(:require).with('puppet/interface/v0.0.1/bar')
       subject["bar", '0.0.1']
     end
   end
 
   describe "::interface?" do
     before :each do
       subject.instance_variable_get("@interfaces")[:foo]['0.0.1'] = 10
     end
 
     it "should return true if the interface specified is registered" do
       subject.interface?("foo", '0.0.1').should == true
     end
 
     it "should attempt to require the interface if it is not registered" do
       subject.expects(:require).with('puppet/interface/v0.0.1/bar')
       subject.interface?("bar", '0.0.1')
     end
 
     it "should return true if requiring the interface registered it" do
       subject.stubs(:require).with do
         subject.instance_variable_get("@interfaces")[:bar]['0.0.1'] = 20
       end
       subject.interface?("bar", '0.0.1').should == true
     end
 
     it "should return false if the interface is not registered" do
       subject.stubs(:require).returns(true)
       subject.interface?("bar", '0.0.1').should == false
     end
 
     it "should return false if there is a LoadError requiring the interface" do
       subject.stubs(:require).raises(LoadError)
       subject.interface?("bar", '0.0.1').should == false
     end
   end
 
   describe "::register" do
     it "should store the interface by name" do
       interface = Puppet::Interface.new(:my_interface, '0.0.1')
       subject.register(interface)
       subject.instance_variable_get("@interfaces").should == {:my_interface => {'0.0.1' => interface}}
     end
   end
 
   describe "::underscorize" do
     faulty = [1, "#foo", "$bar", "sturm und drang", :"sturm und drang"]
     valid  = {
       "Foo"      => :foo,
       :Foo       => :foo,
       "foo_bar"  => :foo_bar,
       :foo_bar   => :foo_bar,
       "foo-bar"  => :foo_bar,
       :"foo-bar" => :foo_bar,
     }
 
     valid.each do |input, expect|
       it "should map #{input.inspect} to #{expect.inspect}" do
         result = subject.underscorize(input)
         result.should == expect
       end
     end
 
     faulty.each do |input|
       it "should fail when presented with #{input.inspect} (#{input.class})" do
         expect { subject.underscorize(input) }.
           should raise_error ArgumentError, /not a valid interface name/
       end
     end
   end
 end