["Journal of Research on Adolescence, Volume 36, Issue 3, September 2026. ", "\nAbstract\nGender–sexuality alliances (GSAs) provide critical support for 2SLGBTQ+ youth, yet the role of advisors—particularly in their self‐efficacy to address race‐, ethnicity‐, and immigration‐related issues, including how these intersect with sexual and gender identity, a construct we term racial‐ethnic, immigration, and intersectional self‐efficacy (REISE)—remains understudied. This study examined (a) which advisor‐, GSA‐, and school‐related factors are associated with advisors' REISE, and (b) how this efficacy relates to youth members' socioemotional experiences. Data were collected from 627 GSA members at three time points and from 64 advisors at one time point from 51 GSAs in Massachusetts, New York City, and California. Advisors' REISE was associated with personal, advisor‐related, contextual, GSA‐related, and school‐related factors, and with GSA youth members' reported school experiences. Advisors of color and those who felt more confident in supporting GSA members—particularly regarding 2SLGBTQ+ issues—reported higher REISE. Higher REISE was also observed in advisors of GSAs with a greater proportion of members of color, in schools offering culturally responsive curricula and race/ethnicity‐focused events, and of GSAs characterized by open and inclusive climates. The extent to which advisors felt more efficacious was unrelated to how long they had served as a GSA advisor or to the frequency of GSA meetings. Moreover, random‐intercept multilevel models showed that members with advisors who reported higher REISE perceived their GSAs and advisors to be more supportive at that same time point. Beyond the GSA itself, advisors' higher REISE also predicted higher positive affect and lower victimization among members, with these benefits lasting for several months. These associations did not vary by GSA members' race/ethnicity or victimization, suggesting that advisor REISE may serve as a universal protective resource for diverse youth.\n"]