Over the last decade, standards for when and how to undertake a wide range of medical interventions have poured forth from medical specialty groups, commercial and nonprofit organizations, and state and federal panels. Known by a variety of names—from practice parameters to clinical guidelines—and intended for a range of purposes—from diminishing the incidence of maloccurences in hospitals to cutting the costs of health care—these guidelines share one important feature: the intention of decreasing the range of variation in medical practice. Such standardization immediately appeals to anyone interested in improving the quality of health care and, in particular, reducing inappropriate medical interventions, in light of the difficulties for a conscientious physician today in adhering to the best standard of practice when faced with ever increasing medical knowledge and the growing number and complexity of diagnostic, preventive, and therapeutic interventions.