The health care community must address criticisms that the quality of health care in the United States is inadequate. This article describes one successful program in a large, not-for-profit health plan in which key aspects of physician specialty groups' performance are evaluated by both patients and the generalists who refer them. The results of the evaluations, which include comparisons among practices, are provided to the specialist groups, who use the information to improve their quality of care. The authors also discuss features that are essential to the success of such quality-improvement programs.