In a political and economic context, a basic goal of health care is: appropriate outcomes from appropriate services for appropriate costs in the context of a societal agreement on resources available. One way that the issue of appropriate medical services may be approached is through guidelines established by professional societies. The work of the American College of Physicians (ACP) in its Clinical Efficacy Assessment Project (CEAP) and its development of guidelines is described. In order that guidelines be effective and that practice behavior be modified to conform more to data on effectiveness and less to habit, four components are necessary: valid information from a credible source backed by an incentive within a receptive environment. Each of these components is described.