Module.used_modules was added in #7418. But I think `Module.used_refinements` is more useful or at least complementary. Refinements were implemented in TruffleRuby, and I found Module.used_refinements so useful that I left it there. Instead of listing namespace modules (arguments to #using), it lists the refinement modules: ~~~ ruby module Json refine Integer do def to_json to_s end end refine String do def to_json inspect end end end module Fact refine Integer do def fact self <= 1 ? 1 : self * (self-1).fact end end end using Json p Module.used_modules # => [Json] p Module.used_refinements # => [#<refinement:Integer@Json>, #<refinement:String@Json>] using Fact p Module.used_modules # => [Json, Fact] p Module.used_refinements # => [#<refinement:Integer@Fact>, #<refinement:Integer@Json>, #<refinement:String@Json>] ~~~ This shows which classes are refined and by which refinement namespace. It also shows if a class has multiple active refinements in the scope. And, last but not least, the name of the method is contains "refinements". I find `used_modules` hard to remember and it doesn't sound related to refinements from the name (while looking at the Module's methods).