Development of novel devices depends on the size, structure and controlled morphology of nanomaterials. Understanding the growth parameters and growth mechanism of nanostructured materials is essential. ZnO is one of the most promising and important semiconductor materials for its semiconducting characteristics. Variety of ZnO nanostructures such as nanowires, nanorods, nanotubes, nanorings, nanohelixes, nanosprings, nanobelts can be prepared by using a solidvapour method, vapour liquid solid method and hydrothermal methods under specific growth conditions. ZnO clearly demonstrates its versatility in its structures and characteristics. This chapter also reviews the novel nanostructures of ZnO synthesized by solid-vapour method, vapour-liquid-solid method and hydrothermal method and their growth mechanisms. The applications of ZnO nanostructures as gas sensing, field effect transistors, solar cell, piezoelectric and EM detector is discussed. © Springer-Verlag Berlin Heidelberg 2010.