Phase Change Materials (PCM) plays an important role in energy conservation, which is very attractive because of its high storage density with small temperature change. In this paper an attempt made to review number of paper based on Phase Change Materials (PCM) in various field of thermal energy storage systems and its applications. The Phase Change Material is the latent heat storage material. As the source temperature raises the chemical bonds within the PCM breaks and the material changes its phase from one phase to another phase. The material begins to melt when the phase change temperature is reached. The temperature then stays constant until the melting process is finished. Thermal Energy Storage deals with the storing of energy by cooling, heating, melting, solidifying or vaporizing a material, the energy becoming available as heat when the process is reversed. Hence it is important to study about phase change materials in thermal energy storage system.Keywords: Phase change materials, Thermal energy storage system, Encapsulation, solar system, Heating and cooling of building
