Progress on a hypertextbook on the theory of computing is presented. The hypertextbook is a novel teaching and learning resource built around web technologies that incorporates text, sound, pictures, illustrations, slide shows, video clips, and--most importantly--active learning models of the key concepts of the theory of computing into an integrated resource. Active learning models currently exist for finite state automata, regular expressions, regular grammars, the pumping lemma for regular languages, context-free grammars, LL(1) parsing, and program execution. The seamless interweaving of these components into a browser-ready whole will help realize the goal of integrating visualization aids into theory courses.