Wide-band-gap semiconductors have been a research topic for many decades. However, it is only in recent years that the promise for technological applications came to be realized; simultaneously an upsurge of experimental and theoretical activity in the field has been witnessed. Semiconductors with wide band gaps exhibit unique electronic and optical properties. Their low intrinsic carrier concentrations and high breakdown voltage allow high-temperature and high-power applications (diamond, SiC etc.). The short wavelength of band-to-band transitions allows emission in the green, blue, or even UV region of the spectrum (ZnSe, GaN, etc.). In addition, many of these materials have favorable mechanical and thermal characteristics.These proceedings reflect the exciting progress made in this field. Successful p-type doping of ZnSe has recently led to the fabrication of blue-green injection lasers in ZnSe; applications of short-wavelength light-emitting devices range from color displays to optical storage. In SiC, advances in growth techniques for bulk as well as epitaxial material have made the commercial production of high-temperature and high-frequency devices possible. For GaN, refinement of growth procedures and new ways of obtaining doped material have resulted in blue-light-emitting diodes and opened the road to the development of laser diodes. Finally, while the quality of artificial diamond is not yet high enough for electronic applications, the promise it holds in terms of unique material properties is encouraging intense activity in the field.This volume contains contributions from recognized experts presently working on different material systems in the field. The papers cover the theoretical, experimental and application-oriented aspects of this exciting topic.