The Health and Medical Care Archive (HMCA) is the data archive of the Robert Wood Johnson Foundation (RWJF), the largest philanthropy devoted exclusively to health and health care in the United States. Operated by the Inter-university Consortium for Political and Social Research (ICPSR) at the University of Michigan, HMCA preserves and disseminates data collected by selected research projects funded by the Foundation and facilitates secondary analyses of the data. The data collections in HMCA include surveys of health care professionals and organizations, investigations of access to medical care, surveys on substance abuse, and evaluations of innovative programs for the delivery of health care. Our goal is to increase understanding of health and health care in the United States through secondary analysis of RWJF-supported data collections.