This book was motivated in large part by the tremendous interest shown in nitride semiconductors by the scientific community in recent years. The interest is due to the wide range of commercially viable industrial applications such as visible and ultraviolet optoelectronics. The aim of thisbook is to elucidate the physics of nitride-based materials and related devices, and to provide to graduate students and young researchers a rapid introduction to this burgeoning field. Chapters of tutorial style are of medium length, and have been commissioned from some of the very best experts oneach topic, both from academia and from industry. All aspects arising from the dual challenges of achieving high-quality, single crystal material and engineering optoelectronic devices are addressed. In the first chapters, the reader will learn about the nitrides in the context of othersemiconductors, and will be exposed to the methods used to grow these materials. The chapters which follow discuss the materials' performance from the point of view of electronic transport, optical and structural properties. Finally, an extensive review of device applications is provided in thearea of modern transistors, ultraviolet detectors and light emitters.