The author provides a detailed overview of the missions, accomplishments, current strategies, and unique institutional role of those U.S. private foundations that have a significant focus on health, especially those that emphasize the support of medical education. The major foundations of this kind are identified, their contributions during this century are described, and their current finding strategies and directions are listed. The author indicates the history of foundation giving during this century, discusses in detail the characteristics of five major foundations, indicates their influence in the medical education and public health arenas in the United States and around the world, and provides two tables with thumbnail sketches of 31 foundations working in these arenas. She concludes that foundations have offered and continue to offer to government, medical schools, and other health-promoting institutions an array of innovative, less traditional options and the results of pilot programs using these options. In this way, foundations provide challenges and guidance to these institutions to stretch toward better ways of fulfilling their missions. Clearly, foundations cannot fund the cost of reforming medical education and health care for the twenty-first century, but they have a crucial role in leading the way to such reform.