Abstract
ZnO nanowires (or nanorods) have been widely studied due to their unique material properties and remarkable performance in electronics, optics, and photonics. This chapter presents a review of the current research of ZnO nanowires (or nanorods) synthesized by hydrothermal method. We discussed the mechanism of its nucleation and growth taking the effect of different parameters on its growth direction and their final morphology into account. A mixture of zinc nitrate and hexamine as precursor is the most popular. We reported the effect of precursor type and concentration, pH of the growth solution, bath temperature, substrate type and seeded layer, and duration time.