Abstract Lesbian, gay, bisexual, queer or questioning, and those youth with other sexual minority identities (LGBQ+) report riskier alcohol use patterns than their heterosexual peers. This raises concerns that—like patterns found in the general population—early, risky alcohol use may strongly predict later alcohol problems and related deleterious health consequences (e.g., other substance abuse, victimization, poor physical and mental health) that contribute to health disparities among sexual minority adults. The harmful effects of peer victimization (PV; i.e. bullying and sexual harassment) on adolescent psychosocial functioning may be one pathway through which LGBQ+ youth become involved in high-risk alcohol use. In adolescence, heterosexist social norms are strongly enforced through bullying and homophobic sexual harassment. Alarmingly high numbers of LGBQ+ youth experience homophobic peer aggression. Such experiences can lead to internalized heterosexism and sexual minority stress. Sexual minority stress has been strongly associated with increased alcohol use across the lifespan in sexual minority populations. Cross-sectional studies have shown that PV is positively associated with alcohol and other substance use among LGBQ+ adolescents. However, the mechanisms through which PV contributes to negative outcomes and the protective factors that ameliorate those outcomes among LGBTQ+ youth are not well understood. Advances in understanding the effects of PV on LGBQ+ adolescents have been hampered by a dearth of longitudinal and mixed methods studies that include these youth in their samples. Using a mixed methods design, the proposed study will investigate the acute daily and longitudinal effects of PV on LGBQ+ adolescent risky alcohol use, as well as identify potential buffers and risk factors for these outcomes. Data from 500 adolescents (ages 15-17 years, 50% female gender identity, diverse racial composition) will be collected using four longitudinal surveys (baseline, 6-, 12, and 18- month follow-ups), two bursts of daily reports (4-weeks each), and qualitative interviews. Informed by sexual minority stress and psychological mediation theories, the proposed study aims to: (1) identify the psychosocial mechanisms linking PV with alcohol and other substance use among LGBQ+ youth; (2) understand the daily associations between PV and alcohol and substance use; and (3) examine the contexts in which LGBQ+ youth experience PV and gain insight into the psychosocial factors related to PV and substance use. The proposed study utilizes a novel integrative conceptual model that incorporates extant knowledge from research on PV and substance use conducted with heterosexual youth along with factors identified in the LGBQ+ literature, including sexual minority stress and the psychological mediation framework, to clarify the processes implicated in substance use by LGBQ+ youth. Results from this study are critically needed to understand the pathways, proce...