The following study and report, conducted by the Association of American Medical Colleges, uses a microsimulation approach to project the supply and demand for healthcare services and physicians. Study results suggest the demand for physician services is growing faster than supply, with a short fall of 46,100 to 90,400 physicians. Uncertainties regarding how emerging care delivery models and changing care practices might affect physician supply and demand, together with uncertainties regarding how clinicians and care settings will respond to economic and other trends, underscore the importance of ongoing research on potential implications of the evolving health care system for the nation’s physicians.