ryptography be approached, and QKD be appreciated as to its relative merits. Concerning the QIT and QC side, it is important to note that this book purposefully avoids touching on two key issues: the effects of quantum decoherence, and the physical implementation of quantum-gate circuits. These two issues, which are intimately related, are of central importance in the industrial realization of practical, massively parallel quantum computers. In this respect, the experimental domain is still at a stage of infancy, and books describing the current or future technology avenues in QC already fill entire shelves. Notwithstanding long-term expectations and coverage limitations, it is my conviction that this present book may largely enable telecom scientists to gain a first and fairly complete appraisal of both IT and QIT. Furthermore, the reading experience should substantially help one to acquire a solid background for understanding QC applications and experimental realizations, and orienting one's research programs and proposals accordingly. In large companies, such a background should also turn out to be helpful to propose related positioning and academic partnership strategy to the top management, with confident knowledge and conviction. Acknowledgments The author is indebted to Dr. Ivan Favero and Dr. Xavier Caillet of the Université Paris-Diderot and Centre National de la Recherche Scientifique (CNRS, www.cnrs. fr/index.html) for their critical review of the manuscript and very helpful suggestions for improvement, and to Professor Vincent Berger of the Université Paris-Diderot and Centre National de la Recherche Scientifique (CNRS, www.cnrs.fr/index.html) for his Foreword to this book. Probability basics Because of the reader's interest in information theory, it is assumed that, to some extent, he or she is relatively familiar with probability theory, its main concepts, theorems, and practical tools. Whether a graduate student or a confirmed professional, it is possible, however, that a good fraction, if not all 