To meet the quality, affordability, and access challenges of today's health care system, the Institute of Medicine's (IOM's) Crossing the Quality Chasm report described the critical competencies of a twenty-first-century health care system. A growing body of research suggests that the nation's multispecialty group practices most nearly meet the delivery system challenges set forth by the IOM. A variety of current public and private initiatives and potential policy options could act as catalysts for the development and spread of group practice-based, accountable delivery systems that are effective and efficient.