["Analyses of Social Issues and Public Policy, Volume 26, Issue 2, August 2026. ", "\nAbstract\nThis mixed‐methods study examines the experience of the impostor phenomenon in a racially/ethnically and sexually diverse sample of undergraduates in majors related to science, technology, engineering, and math (STEM). Guided by an intersectionality framework, we examined whether experiences of the impostor phenomenon differ at the intersection of race, ethnicity, and sexual identity. Survey data from undergraduate STEM students (N = 735), consisting of 559 (76%) racial/ethnic minorities, 169 (23%) lesbian, gay, bisexual, transgender, and queer/questioning (LGBTQ) individuals, and 119 (16.2%) racialized LGBTQ individuals, revealed racial/ethnic and LGBTQ differences in the impostor phenomenon. Findings also suggest that STEM students with at least one mentor reported lower levels of impostor phenomenon. This finding was not moderated by race/ethnicity or sexual identity, suggesting that mentoring may be a form of social support that offers equivalent benefits to students from diverse STEM educational backgrounds. To supplement the quantitative findings, we collected open and closed‐ended data from participants. Thematic analysis of these data provides insight into the range of coping strategies STEM students use when experiencing the impostor phenomenon. Implications and recommendations for research, theory, and policy are further discussed.\n\nPublic Significance Statement\nThis study suggests that racial/ethnic or sexual minority college students in STEM often experience impostor feelings, which can impact their success. However, having one or more mentors may reduce these feelings across all groups. Expanding mentorship opportunities may help promote equity and inclusion in STEM education and policy.\n"]