This book examines the fundamental physics underlying this rich complexity of photoelectronic properties of semiconductors, and will familiarize the reader with the relatively simple models that are useful in describing these fundamentals. Following introductory material on the basic concepts, the book moves on to consider a wide range of phenomena, including photoconductivity, recombination effects, photoelectronic methods of defect analysis, photoeffects at grain boundaries, amorphous semiconductors, photovoltaic effects, and photoeffects in quantum wells and superlattices.