Energy storage has the potential to revolutionize electricity consumption and generation. This is because economic and efficient storage delinks the supply and demand sides of the electricity and other energy systems by introducing a viable inventory mechanism. A major technical challenge in this sphere is that useful energy is lost every time energy is converted from one medium to another. An equally important issue arises from the mixture of market-based competition and traditional cost-of-service regulation in many parts of the world. This hybrid regulatory design can create impediments to fully capturing the value of all of the services that storage technologies can provide. A related issue that lies between the economic, regulatory, and technical issues is the wide variety of storage technologies available today. These technologies can be amenable to different applications, depending on their physical characteristics, and understanding the tradeoffs between the different technologies is vitally important for making storage investments viable. On the other hand, energy storage, mainly thermal energy storage (TES), is also used to decrease the energy demand of buildings and industry or to improve energy efficiency of energy system. The article in this volume touch on these and other issues related to energy storage.