For families facing a serious or complex medical problem, the choice of hospital can be critical. Yet until 1990, when U.S. News & World Report introduced “Best Hospitals,” they had few tools or resources beyond a doctor’s recommendation to inform their decision. The annual assessments initially took the form of alphabetized lists in 12 specialties, but hospitals were ranked within each specialty starting in 1993. This year’s “Best Hospitals” draws from a universe of 4,825 medical facilities.* We use the hospital definitions supplied by the American Hospital Association (AHA) in its annual survey, which is the source of some of the data used in the Best Hospitals rankings. Under rare circumstances, we will combine two or more AHA hospitals for rankings purposes when they function as one but report separately to the AHA for specific, meaningful, and verifiable reasons.