using_concern.rb

require 'active_support' 
module MyConcern
  extend ActiveSupport::Concern
  def an_instance_method; "an instance method"; end

  module ClassMethods
    def a_class_method; "a class method"; end
  end 
end

class MyClass 
  include MyConcern
end

MyClass.new.an_instance_method # => "an instance method" 
MyClass.a_class_method # => "a class method"