Zinc oxide is a direct, wide bandgap semiconductor material with many promising properties for blue/UV optoelectronics, transparent electronics, spintronic devices and sensor applications. ZnO has been commonly used in its polycrystalline form for over a hundred years in a wide range of applications: facial powders, ointments, sunscreens, catalysts, lubricant additives, paint pigmentation, piezoelectric transducers, varistors, and as transparent conducting electrodes . Its research interest has waxed and waned as new prospective applications revive interest in the material, but the applications have been limited by the technology available at the time. ZnO can be grown on inexpensive substrate, such as glass, at relatively low temperatures. Nanostructures, such as nanowires and nanorods, have been demonstrated. These structures are ideal for detection applications due to its large surface area to volume ratio.Recent improvements in the growth of high quality, single crystalline ZnO in both bulk and epitaxial forms has renewed interest in this material. Significant efforts in the last few years have been aimed at controlling conductivity and improving crystal quality. However, in order to fully realize ZnO devices, additional material and process development issues must be overcome. The purpose of this book is to provide an overview of recent progress in ZnO research and identify future areas that need work.