This third edition, like its two predecessors, provides a detailed account of the basic theory needed to understand the properties of light and its interactions with atoms, in particular the many nonclassical effects that have now been observed in quantum optical experiments The earlier chapters describe the quantum mechanics of various optical processes, leading from the classical representation of the electromagnetic field to the quantum theory of light The later chapters develop the theoretical descriptions of some of the key experiments in quantum optics Over half of the material in this third edition is new It includes topics that have come into prominence over the last two decades, such as the beamsplitter theory, squeezed light, two photon interference, balanced homodyne detection, travelling wave attenuation and amplification, quantum jumps, and the ranges of nonliner optical processes important in the generation of nonclassical light The book is written as a textbook, with the treatment as a whole appropriate for graduate or postgraduate students, while earlier chapters are also suitable for final year undergraduates Overproblems help to intensify the understanding of the material presentedRodney Loudon, Professor of Theoretical Physics, Department of Electronic Systems Engineering, University of Essex