Shuji Nakamura's development of commercial light emitters from Gallium Nitride and related materials has recently propelled these materials into the mainstream of interest. It is very rare that a breakthrough of such proportion can be converted so quickly into successful commercial products. One factor for this success is Shuji Nakamura's hard work, another factor is Nichia's enlightened founder, Chairman and joint owner, Nobuo Ogawa without whom Nakamura probably could not have done this work, other factors are Professor Pankove's and Professor Akasaki's pioneering work. The amazing speed of GaN breakthroughs caused an information gap. There is much less information available on GaN then on silicon or GaAs, and most current semiconductor text books do not even mention Gallium Nitride. One of the aims of the present book is to close this information gap, another important aim is to provide a report on the development of Gal­ lium Nitride based light emitters and lasers and their properties. Both aims are rapidly moving targets: recent results near the end of the book even report, that InGaN lasers might become the first commercial lasers using self-assembled quantum dots.