Book excerpt: This book covers the full spectrum of activity in the GaN and related materials arena. These semiconductors are finding applications in full-color displays, high-density information storage, white lighting for outdoor or backlit displays, solar-blind UV detectors, high-power/high-temperature electronics, and covert undersea communications. Progress is been reported in the growth of thick layers on patterned substrates by various methods, leading to lower overall defect concentrations and improved current-voltage and reliability characteristics. The rapidly increasing market for blue/green LEDs is also noted by the entry of a number of new companies to the field. While these emitter technologies continue to be dominated by MOCVD material, there are exciting reports of UV detectors and HFET structures grown by MBE with device performance at least as good as by MOCVD. Topics include: GaN electronic and photonic devices; laser diodes and spectroscopy; electronic devices and processing; quantum dots and processing; novel growth, doping and processing and rare-earth doping and optical emission.