Is a transition to a 100% renewable energy economy possible? A Stanford University team has demonstrated the feasibility of a worldwide transition to a renewable energy economy by 2050. In a recent follow-up study, they show in more detail how this can be accomplished at the national level, specifically, in the United States. A combination of hydroelectric, wind, and solar power technologies currently available could provide the energy needed for all sectors of the US economy to achieve a goal of full decarbonization by 2050. Renewable resources are in ample supply, but variable, so the key challenge is delivering energy when it is needed. Energy storage technologies, such as central station solar thermal electric generation and decentralized electricity and thermal storage in buildings, as well as stronger electricity transmission grids, can negate such obstacles. If a 100% renewable energy economy is technologically feasible, then the main obstacle is political will.