Zinc oxide is a semiconductor whose technological applications are widespread in areas such as optoelectronics, sensors, transducers and biomedical sciences. This material can be prepared at the nanoscale in a variety of shapes and sizes, can be obtained as a metal doped host and also used as a functionalized filler in polymer composites. These characteristics, among many others, make this material suitable to understand nanoscale phenomena conceptually common to other nanocrystalline semiconductors. In this chapter, special focus will be made on recent research of diverse chemical routes for ZnO nanostructures and relevant size and shape dependent optical properties. Also general guidelines on fabrication parameters that affect the properties of ZnO based nanomaterials and their novel applications will be reviewed.