Adolescents' sense of belonging in high school may serve a protective function, linking school-based relationships to positive youth outcomes. To advance the study of sense of belonging, we conducted a mixed method, factor analytic study (Phase 1 focus groups, N = 72; Phase 2 cross-sectional survey, N = 890) to explore the multidimensionality of the sense of belonging construct. Findings suggest that adolescents' sense of belonging involves four distinct school-experience factors: Generalized connection to teachers; connection to a specific teacher; identification and participation in official school-sanctioned activities; and perception of fitting in with peers. Future research should investigate the validity of the proposed sense of belonging subdimensions and longitudinally examine the form and function of disparate adolescent school-based relationships in relation to academic engagement or disengagement processes. (Contains 5 tables, 1 footnote and 2 figures.)