This book presents a quantum framework for understanding inelastic light scattering which is consistent with the classical descriptions of Raman phenomena and Rayleigh scattering, thus creating a unified theoretical picture of light scattering. The Raman effect was discovered in 1928 and has since proved to be one of the most powerful tools to study the molecular structure of gases, liquids, and crystals. The subsequent development of new scientific disciplines such as nonlinear optics, quantum optics,  plasmonics, metamaterials, and the theory of open quantum systems has...