Elliott S. Fisher, M.D., M.P.H., is director of the Center for Population Health at The Dartmouth Institute for Health Policy and Clinical Practice. He is the director of the Dartmouth Atlas of Health Care and a member of the Institute of Medicine of the National Academy of Sciences. Dr. Fisher’s research has focused on exploring the causes of the twofold differences in spending observed across U.S. regions and health care systems, on understanding the consequences of these variations for health and health care, and on the development and testing of approaches to performance measurement and payment reform that can support improvement. His current policy work has focused on advancing the concept of accountable care organizations (ACOs) and includes codirecting, with Mark McClellan, a joint Brookings–Dartmouth program to advance ACOs through research, coordination of public and private initiatives, and the creation of a learning collaborative that includes several pilot ACO sites across the United States.