This book provides a thorough introduction to the field, developed from Turro's bestselling text "Modern Molecular Photochemistry'. It is developed from Turro's best-selling text for three decades - "Modern Molecular Photochemistry". The book provides for the first time in any photochemical text, a fundamental description of electronic spin and its impact on photochemical and photophysical processes, described with a vector model that is intuitive, pictorial and powerful. Also for the first time in any photochemical text, the concepts of electronic energy transfer and electron transfer are treated from a common foundation and set of principles. The progress in theoretical and experimental electron transfer are covered in depth.This text develops photochemical and photophysical concepts from a set of familiar principles. It provides indepth coverage of electronic spin, and the concepts of electronic energy transfer and electron transfer, and the progress that has been made in theoretical and experimental electron transfer.