This is a gem of a book. It comprehensively covers the subject and is a pleasure to read. I highly recommend it for courses on photochemistry and for practitioners in all areas of the photosciences. Having been afforded the opportunity to comment on sections of the book prior to its publication, I am well aware of the care that went into providing the accurate and up to date descriptions of physical concepts and reaction mechanisms that are the hallmark of this book. The knowledge explosion that occurred in the course of the preceding half century has led some to conclude that the photochemistry of organic molecules is a mature field. By describing the intricacies of photophysical and photochemical responses of a cornucopia of selected molecules this book dispels this notion.