Alan Turing, pioneer of computing and World War II code-breaker, was one of the most important and influential thinkers of the twentieth century. The astonishing output of his tragically short life included the universal Turing Machine (the theoretical foundation of all modern computing), the electro-mechanical 'bombes' used at Bletchley Park to decipher the Enigma code, his ground-breaking design for an electronic stored-programme computer, and work on artificial intelligence and artificial life so revolutionary that he can claim to be the founding father of these disciplines. In this book, Turing's key writings in all these subjects are made easily accessible for the first time. Lectures, scientific papers, top secret wartime material, correspondence, and broadcasts are introduced and set in context by Jack Copeland, Director of the Turing Archive for the History of Computing.