The article depicts the evolution of Managed Care. A first part describes and evaluates the Managed Care experience in the U S. After a review of the major events that led to Managed Care in the U.S., the paper expands on cost-control mechanisms, changes in the medical practice and their impact on patient’s health. In the second part, the article proposes a theoretical interpretation of the development of HMOs based on the cost transaction theory, and uses the W.H.O evaluation grid to outline the orientations of the U.S. health care system.