Materials start showing anomalous behaviour when their size approaches nanometer range. Nanocrystalline semiconductors are of keen interest due to their size dependent properties. Their properties can be controlled by controlling the size of the nanoparticles. The MSe [M = Cd, Zn and Sn] semiconductors generally have wide optical gap gap lying in solar energy spectrum. These materials possess the necessary criteria to make them potential candidates in photo-electrochemical solar cells. The main advantage of these semiconductors is that, they make up the group of direct wide band gap semiconductors, which is very important for both emissive as well as photovoltaic applications. The work discussed in the present book deals with the deposition of nanocrystalline MSe thin films and some useful measurements on structural, optical and electrical properties of these semiconductors. The effect of different deposition parameters such as pressure, substrate temperature and annealing has been discussed on the structural, optical and electrical properties of these films.