Quantum Optics offers a very wide coverage of fundamental phenomena encompassing quantum mechanics and physical optics. Quantum optics allows the engineers and scientists to perform research in laser physics and quantum optics. This book covers various topics including electromagnetic field quantization, quantum coherence theory, models of atom-field interaction, resonance fluorescence, laser theory and input-output theory (application in non-linear optics). The purpose of this book is to offer various exciting advances in the field of quantum optics. Presently, quantum optics is being applied in many applications which involve electronics, climate control, space science, medical science and industrial sectors. This book put emphasis on basic concepts and applications of quantum optics and its associated fields, so as to facilitate the students and researchers to perform their research in this amazing field. The topics of this books are offered in a didactic and unified manner. The book exhibits a pedagogical and clear demonstration of topics. It successfully stabilizes the theoretical and quantum aspects of quantum optics with modern relevant experiments. The book is equally useful for students, scientist, teachers and industrialists from various backgrounds including quantum mechanics, optical physics, electromagnetism and many multidisciplinary fields.