The aim of this book is to provide guidance and introduce the broad literature in all the various aspects of quantum information theory. The topics covered range from the fundamental aspects of the theory, like quantum algorithms and quantum complexity, to the technological aspects of the design of quantum-information-processing devices. Each section of the book consists of a selection of key papers (with particular attention to their tutorial value), chosen and introduced by leading scientists in the specific area. An entirely new introduction to quantum complexity has been specially written for the book.