As a functional oxide material, zinc oxide (ZnO) has substantial research importance for its superior optical and electrical properties, which may lead a race for the innovation in the next decade. The fabrication, characterization, and applications of ZnO based nanostructures are the central issues of this book. Emphasis is devoted to realize the high- efficient, mechanical-flexible and wavelength- tunable lasers and field emitters by ZnO based nanostructures.