The fourth International Conference on Future Energy Systems (ACM e-Energy), to be held in Berkeley, CA in May 2013, aims to be the premier venue for researchers working in the broad areas of computing and communication for smart energy systems (including the smart grid), and in energy-efficient computing and communication systems. By bringing together researchers in a high-quality single-track conference with significant opportunities for individual and small-group interaction, it will serve as a major forum for presentations and discussions that will shape the future of this area.