The development of practice guidelines has become a key health care quality issue in the 1990s. A growing doubt that the benefits of health services are worth the price we now pay has brought the development of such guidelines to the forefront of public and professional agendas. This questioning is in turn caused by wider appreciation of several facts: Scientific evidence is lacking to document the efficacy of much of medical practice. There is significant variation in the use of medical and surgical procedures. There are widespread errors of omission as well as commission in medical practice. All of the above suggest quality problems in medical care and imply that more specific, rigorous, standardized, and structured approaches to medical care could improve both quality and value while managing costs more effectively. Methods for the development of guidelines are reviewed. Guidelines can be used effectively and impartially for education, reimbursement, quality improvement, and research. For this form of quality improvement to succeed, physicians must participate actively in the development of guidelines and be committed to their consistent use. It is suggested that practice guidelines can provide legal protection as well as more efficient and effective health care.