When we were preparing the first edition of this book, the concept of de coherence was known only to a minority of physicists. In the meantime, a wealth of contributions has appeared in the literature - important ones as well as serious misunderstandings. The phenomenon itself is now experimen tally clearly established and theoretically well understood in principle. New fields of application, discussed in the revised book, are chaos theory, informa tion theory, quantum computers, neuroscience, ...