Semiconductor nanoparticles have drawn much attention due to their size dependent properties. Cadmium Sulphide (CdS), due to its large Bohr exciton diameter, has applications in various areas like optoelectronics, photo catalysis, biological assays,optical data storage and sensing. The optical properties of CdS nanoparticles capped with different capping agents, synthesized in aqueous and non-aqueous medium are presented in this monograph. As surface states have significant influence on the optical properties, surface passivation is important for improving Photoluminescence property apart from controlling the particle size. Stability and the optical properties of CdS - Polyvinyl Alcohol (PVA) nanocomposite films are dealt. The effects of electron irradiation and also, a Zinc Sulphide (ZnS) coating on the luminescence properties of CdS nanoparticles are also given. This monograph is specially targeted to researchers working in the field of semiconductor nanoparticles as well as postgraduate students of Physics, Chemistry, Electrical and Materials Engineering.