Although we designed Scratch primarily as a means for personal expression, a growing number of high schools and colleges (including Harvard and Berkeley) are using Scratch as an introduction to computer science and programming. The Scratch4CS project explores the question: "Can we extend Scratch so that it is suitable for a full-semester introduction to programming and computational thinking?" This question is particularly relevant now since there are several initiatives underway to rethink introductory computer science courses and advanced-placement exams.