Wide bandgap light emitters include laser diodes and light-emitting diodes (LED), the most modern diodes widely used in current technologies as microelectronics and optoelectronics. Rapid advances have been made during the last few years, with the result that more research is devoted to applications in line with the expanding market for optoelectronics. This volume deals with recent research results on wide bandgap light emitting materials, introducing new concepts for devices based on these materials. The editors, scientists with the best reputations, have invited authors from different institutions who are acknowledged researchers in the field as well as being involved in industrial applications. They represent several lines of research: III-nitride compounds, ZnO and ZnSe, the most promising materials for device applications..