Lately, Matz (the inventor of Ruby) has been focusing, like many people in the technical world, on mobile devices. How can Ruby be used to program in an increasingly mobile world? The answer is mRuby, a mobile-oriented version of Ruby, on which Matz and others are working. In this talk, Matz introduces mRuby, and describes his considerations and thoughts on the topic. What is truly crucial to keep in the language, and what can be left out?