Quantum Optics is a rapidly progressing field well suited to probe the many fundamental issues raised by the subtleties of quantum physics. This book consists of a collection of reviews and papers that highlight the most important challenges faced in this area of research, including topics such as cavity QED, quantum entanglement, decoherence, matter waves and nonlinear optics. It will be a source of reference for all those who wish to familiarize themselves with the latest developments in the field.