The Health Maintenance Organization (HMO) Act of 1973, which sought to balance quality health care against cost-containment efforts, gave rise to the rapid growth of managed health care systems, especially HMOs. This article traces the legislative history of HMOs, the inclusion of mental health care benefits, the recognition of psychologists under Medicare law as autonomous health care providers, and other legislative issues. The expansion of managed health care organizations in the national health care system has generated considerable debate about the quality of physical health and mental health services, access to needed care, and the administrative and financial operations affecting consumer-provider relations.The true beginning of the modern concept of managed health care is somewhat obscure. There are events in the early 1900s that could lead one to agree to a date like 1904 or 1906. With the Ross-Loos Clinic becoming operational in 1929, that year has a good claim. The Depression-era efforts of Kaiser Permanente became fully recognized in 1945, so that date stands out. The passage of the federal Health Maintenance Organization Act in 1973 can be viewed as a central date as well.The lumbering and mining industries operating in the Pacific Northwest in the early 1900s provided the site of an early prepayment plan-that is, the provision of a set package of health care services by an identified provider for a preestablished fee. The Western Clinic, a fee-for-service partnership in Tacoma, Washington, is reported to be one of the first prepaid group practices. In 1906, two physicians contracted to provide medical care for lumber employees for 50« per individual per month. Physicians in private practice in Tacoma, in opposition to the prepaid concept, organized the Pierce County Medical Service Bureau and attempted to limit competition and became a predecessor of county medical societies (Bennett, 1988;Flinn, McMahon, & Collins, 1987).The combination of prepayment schemes with group prac-