The Future of Energy Storage study is the ninth in the MIT Energy Initiative’s Future of series, which aims to shed light on a range of complex and vital issues involving energy and the envi-ronment. Previous studies have focused on the role of technologies such as nuclear power, solar energy, natural gas, geothermal, and coal (with capture and sequestration of carbon dioxide emissions), as well as systems such 
as the U.S. electric power grid. Central to all these studies is understanding the role these particular technologies can play in both decar-bonizing global energy systems and meeting future energy needs. Energy storage will play  an important role in achieving both goals by  complementing variable renewable energy (VRE) sources such as solar and wind,  which are central in the decarbonization  of the power sector.