In this work I have discussed simple wet chemical method and electrochemical method to synthesize variety of ZnO nanostructures. The fabricated nanostructures included in this monograph are: ZnO nano-pyramids, octahedron and nanodiscs. The growth mechanisms of the nanostructures have been discussed in detail to provide an in depth understanding of the wet chemical and electrochemical growth mechanisms of nanostructures. The morphological and structural properties were discussed using the FESEM, TEM and X-ray diffraction studies. The compositional analysis has been enunciated using EDXS. The optical absorption property of the nano ZnO has been studied from the UV-VIS spectrum. I have also discussed the method of determining band gap of semiconductors. The photo-luminescence has been elaborated in the view of the PL spectrum of the synthesized materials. The mechanism of the emission has been discussed and the band-diagram has been illustrated. Finally their applications in optoelectronics have been highlighted. I hope this work will be very useful for the ZnO nano-researchers working in the application of ZnO in optoelectronics.