The definition of "photonics" has been broadened in recent years to include nonlinear and quantum optics, today usually based on laser light. This book covers the fundamental properties of photon and light beams, both experimentally and theoretically. It covers the essentials of linear interactions and most of the nonlinear interactions between light and matter in both the transparent and absorbing cases. It also provides a basic knowledge of modern lasers, as well as the principles of nonlinear optical spectroscopy. It is self-consistent and enriched by a large number of calculated illustrations, examples, and descriptive tables. Graduate students in physics and electrical engineering, as well as other sciences, will find this book a thorough introduction to the field, while for lecturers and scientists it offers a rich source of useful information and a ready-to-hand reference. About 4000 references open access to original literature.