This article brings attention to the rarefied world of elite boarding schools. Despite their reputation for excellence, these unique educational institutions remain largely outside the gaze of educational researchers and the scope of public debates about education. One reason for this absence is a lack of knowledge about what exactly defines an elite boarding school and the characteristics that stand them apart from other schools in significant ways. Drawing on a review of the relevant literature, the article outlines five criteria by which elite boarding schools can be identified: typologically elite, scholastically elite, historically elite, geographically elite, and demo-graphically elite. Although the "elite" status of any given school in any of these criteria may be open to debate, it is the particular combination of these five dimensions that defines an elite boarding school. After a discussion of these five characteristics, the article outlines some implications for future research that considers elite boarding schools as an integral part of the educational system in the United States and presents some of the challenges facing the study of privilege. (Contains 17 notes and 1 table.)