Project Summary: A large proportion of new HIV infections occur in the context of primary partnerships among men who have sex with men (MSM), who are themselves disproportionately vulnerable to HIV, suggesting a need to study factors that contribute to this disparity. Intimate partner aggression (IPA) and substance use (SU) are two such factors that are strongly associated with HIV risk behaviors within primary partnerships (e.g., condomless anal sex, breaks in monogamy/non-monogamy relationship agreements), but despite robust evidence that the effects of IPA and SU likely overlap in their influence on HIV risk, formative knowledge on how IPA and SU predict HIV risk in tandem remains missing. This gap in the literature critically limits the foundational knowledge base by which couple-based interventions (which have shown promise in preventing HIV among MSM) can be developed, tested, and optimized. The proposed mixed methods research will: a) conduct complex, multi-level analyses to disentangle the individual, interactive, and dyadic effects of IPA and SU among a large sample of male couples (Aim 1; N=728 couples), and b) collect qualitative data via in-depth interviews to contextualize quantitative effects using the lived experience of men in relationships with other men (N=35) experiencing IPA/SU (Aim 2). Key determinants of risk from quantitative, secondary data analyses (Aim 1) and qualitative, primary data analyses (Aim 2) will be compared to existing interventions to identify prevention gaps and formative targets for future development. The research arm of the present proposal is an ideal fit for the NIH mission since it will document novel pathways to HIV risk among MSM and support future proposals aimed at translating present findings into novel HIV prevention targets -- a critical next step. Although the applicant possesses existing foundational competencies in couple research, psychosocial determinants of health, and advanced quantitative methods, these skills have been accrued via research with cisgender and heterosexual couples. This fellowship will therefore support her in gaining critical new competencies in HIV research, qualitative methods, grantsmanship/publication, and sexual and gender minority (SGM) health by releasing her from grant-related responsibilities currently funding her post-doc appointment. These training and experiential research activities will imbue the applicant with the tools to grow her program of research among male couples and advance towards a career as a NIH-funded independent clinical scientist. Northwestern University’s Institute for Sexual and Gender Minority Health and Wellbeing (ISGMH) is an ideal environment for this fellowship because of the suite of technical, mentorship, intellectual, and instrumental resources it affords to early career researchers. Thus, ISGMH and the present proposal will interact to support the applicant in progressing towards her long-term career goals by providing avenues thr...