Although there are several excellent books covering a few of the specialized areas of photobiology, at the present time there is no book that covers all areas of the science of photobiology. This book attempts to fill this void. The science of photobiology is currently divided into 14 subspecialty areas by the American Society for Photobiology. The first 14 chapters of this book deal with those subspecialty areas, each written by a leader in the field. Chapter 15, entitled "New Topics in Photobiology," highlights areas of research that may be desig- nated subspecialties of photobiology in the future. This book has been written as a textbook to introduce the science of photobiology to advanced undergraduate and graduate students. The chapters are written to provide a broad overview of each topic. They are designed to contain the amount of information that might be presented in a one- to two-hour general lecture. The references are not meant to be exhaustive, but key refer- ences are included to give students an entry into the literature. Frequently a more recent reference that reviews the literature will be cited rather than the first paper by the author making the original discovery. Whenever practical, a classroom demonstration or simple laboratory exercise has been provided to exemplify one or more major points in a chapter.