40 years into the pandemic, stigma remains the most challenging barrier for HIV prevention. A quarter of people living with HIV remain untested, depriving them of opportunities to enter the HIV prevention continuum and access evidence based prevention tools. Testing is particularly low in gay and bisexual men who have sex with men (MSM) who face additional discrimination on account of their same sex behaviors. Stigma can be internalized or anticipated but it is most pernicious when it is enacted in healthcare settings, as this directly bars care access while also discouraging future care seeking. Enacted healthcare stigma is notoriously difficult to measure, as few providers willingly report discriminatory behavior and patients lack the medical knowledge to assess the appropriateness of care. Our solution is to conduct unannounced standardized patient (SP) visits to measure and address enacted healthcare stigma. SPs are actors hired from the local community and trained to present standardized, unannounced disease cases in area clinics for the purposes of evaluation and feedback. Their ability to objectively document provider behaviors through unannounced visits presents an elegant solution to the common tendency of providers to alter behaviors under observation. By randomly varying the sexual orientation and HIV status of presented cases, our technique obtains discrete measures of HIV, sexual, and intersectional stigma. Results of an initial round of SP visits are shared with advisory boards of providers and MSM to solicit their views on stigma drivers which inform a tailored stigma reduction training for study providers which is then evaluated in a second round of visits. Our team has conducted an NIH-funded pilot randomized control trial (RCT) in southern China that demonstrated high feasibility and acceptability of the SP approach for measuring and reducing stigma (R34MH121251). This R01 application follows on the success of the R34 to propose a fully powered cluster RCT using tools, lessons, and experience gained form our pilot. This trial will newly include rural clinics to expand generalizability and will also explore future implementation potential of our intervention with regional policy makers. Our interdisciplinary team combines expertise in HIV prevention, stigma, LGBT health, standardized patient research, and medical education to investigate the following aims: 1) Conduct a baseline round of SP visits to inform the design of a SP-informed stigma reduction intervention with support from MSM and provider community advisory boards; 2) implement the intervention in treatment arm clinics and evaluate its impact on enacted stigma and clinic-level HIV testing volume and 3) conduct qualitative interviews with stakeholders (providers, MSM, health officials) to help inform the design of a Implementation Blueprint to guide potential future adopters in assessing its suitability and their team readiness to implement a SP-informed stigma intervent...