RESUMEN
Despite the prevalence of vertical integration, data and research focused on identifying and describing health systems are sparse. Until recently, we lacked an enumeration of health systems and an understanding of how systems vary by key structural attributes. To fill this gap, the Agency for Healthcare Research and Quality developed the Compendium of U.S. Health Systems, a data resource to support research on comparative health system performance. In this article, we describe the methods used to create the Compendium and present a picture of vertical integration in the United States. We identified 626 health systems in 2016, which accounted for 70% of nonfederal general acute care hospitals. These systems varied by key structural attributes, including size, ownership, and geographic presence. The Compendium can be used to study the characteristics of the U.S. health care system and address policy issues related to provider organizations.