ntist. Forcefully and crudely stated, "The world is ugly out there," in spite of Alice and Bob's "provably secure" key exchanges (quantum key distribution, QKD). Let one not be mistaken as to the author's intent. Quantum key distribution is most precious as an element in the network security chain; Emmanuel Desurvire is only reminding the community, now with the authority of a telecom professor, that Alice and Bob are exposed, in turn, to higher-level network attacks, and that unless the Internet becomes quantum all the way through, there is no such a thing as "absolute" network security. It is only with this type of cross-disciplined book that elementary truths of the like may be spelled out. A pervasive value and flavor of this book is that the many practical examples and illus- trations provided help the reader to think concrete. Both the classical and quantum sides of information theory may seem difficult, rusty, oblivious, if not forthright mysterious to many engineers and scientists since long-past school graduation. More SO with the quantum side, which is actually a recent expansion of knowledge (as dated after the Shor algorithm "milestone"), and that only a few engineers and scientists had the privilege to be exposed to SO far, prior to beginning their professional careers. Hence, this book represents a first attempt at reconciling old with new knowledge, as destined primarily to mature engineers and scientists, particularly from, but not limited to, the telecom circle. Decision makers from government and industry, investors, and entrepreneurs may also Foreword reap some benefit by being better acquainted with the reality of quantum mechanics and the huge application potentials of QIT, apart from any timeliness consideration. Progress in quantum information theory may be a (very) long-term view indeed, but its future is confined to today's humble steps; called awareness, discipline, imagination, creativity and patience. Thanks to Emmanuel Desurvire's book, many concepts such as quantum information theory