Semiconductor nanostructures are very important as it is the building block of all opto- and nano-electronic devices. In nanostructures carriers are confined in a very small region leading to unique properties exhibited by the material compared to bulk structures. In this book I shall discuss bout the confinement of Carriers in nanostructures and its impact on optical properties in the context of photoluminescence from ZnO nanostructures. I have also discussed about a one dimensional potential approach (PMM) to explain the observed luminescence from ZnO nanoparticles. The Optical emissions have been modeled as transition of carriers from higher quantum states to lower quantum states. This book will be very useful to the researchers working in the area of physics of photoluminescence of semiconductor nanostructures.