PROJECT SUMMARY/ ABSTRACT A resurgent stimulant epidemic among sexual minority men/men who have sex with men, including those living with HIV, could compromise the U.S. Ending the HIV Epidemic goals by interfering with HIV care engagement, adherence, and virologic suppression among sexual minority men living with HIV. Prominent multi-level barriers interfere with HIV virologic suppression among sexual minority men living with HIV, particularly among those who use stimulants. We will digitally recruit at least 1,000 sexual minority men living with HIV, of whom at least 40% will identify as Black/African-American and at least 70% will have active stimulant use to identify multi-level determinants of HIV care engagement, adherence, and virologic suppression among sexual minority men living with HIV, with and without stimulant use. Guided by the social ecological model, we will investigate network factors (HIV status, stimulant use), geospatial determinants (background stimulant use prevalence, EHE region), and other structural factors (intersectional stigma, structural racism) that affect virologic suppression (Aim 1). After recruitment milestones are met, we will perform a nested randomized clinical trial to test a multi-component intervention to improve virologic suppression, adherence, positive affect, and stimulant use among sexual minority men living with HIV who use stimulants (n=300). The intervention, known as reSTART, will combine an evidence-based positive affect intervention delivered through a smartphone app and use of urine point-of- care testing to perform adherence self-monitoring, with motivational messages to improve or maintain adherence delivered via the reSTART app (Aim 2). In Aim 3 of the proposal, we will assess the impact of reSTART on incremental cost per person on virologic suppression and optimal antiretroviral therapy adherence measured via hair tenofovir levels. By this high-impact study’s end, we will have identified multi-level determinants of the treatment continuum among digitally-recruited sexual minority men living with HIV, including among those who use stimulants; and the impact of a multi-component reSTART mHealth intervention using novel point-of-care adherence self- monitoring on HIV virologic suppression, adherence, and cost among a key underserved population.