Health service researchers believe that significant practice variations occur, in part, because there is no strong consensus on best practices for managing a specific condition. The Agency for Health Care Policy and Research (AHCPR) supports the development of science-based clinical guidelines, performance measures, and standards of quality. Since 1992, it has published 6 clinical guidelines and is supporting development of more than 20 others. Each has a consumer version, in English and Spanish, to educate patients and describe care options. Widespread use of these guidelines will improve the quality of health care by assisting providers in making more informed decisions, thereby reducing unnecessary health care practices; will reduce some costs; and will provide feedback on knowledge gaps that merit the attention and support of researchers and policymakers.