The evolution of the movement to enact a program of health insurance for the aged in the United States is examined in this article. The most popular conception of the origins and intent of Medicare is compared with empirical data drawn from the Medicare experience, and it is found to be wanting. The author presents political-economic theory to explain the origins and actual operation of the Medicare program. The dynamics of this social innovation, as seen from the political-economic perspective, are then discussed and their relevance to health policy is shown.