Abstract Dentists can play an important role in the Ending the HIV Epidemic initiative by providing access to HIV testing and facilitating access to HIV prevention services for at-risk populations in geographic hotspots, thus decreasing the incidence of HIV infection. To enhance Diagnosis, we propose to investigate incorporating routine on-site rapid HIV testing into the community health center dental clinics to increase HIV testing rates. To expand the delivery of HIV Prevention services in the dental clinic setting, we will test a patient-level text message (TM) intervention designed to decrease risk in those at high risk for HIV infection. In the developmental UG3 phase, we will conduct qualitative research with CHC dental clinic patients, CHC dental providers and dental teams to gain perspectives and explore facilitators, barriers, and acceptability of integrating rapid HIV testing and TM-delivered prevention into dental clinic visits. This data will be used to tailor the final interventions which will then be pilot tested. This formative work will facilitate intervention adoption and success. In the UH3 trial phase, four CHC dental clinics in a designated geographic hotspot for HIV infection, Suffolk County, MA, will participate in a cluster randomized trial comparing the efficacy of on-site rapid HIV testing delivered in the dental clinic (intervention) to referral for HIV testing by a dental provider (control). When that trial ends, a second RCT among dental clinic patients at high risk for HIV infection will determine the efficacy of a text messaging intervention in increasing repeat testing and reducing HIV risk behaviors. The UG3 Specific Aims are: 1. Investigate barriers and facilitators to on-site rapid HIV testing in CHC dental clinics by conducting interviews with dental patients (N=32) and dental providers (N=8); and focus groups with dental teams (N=4); 2. Develop and implement comprehensive training on rapid HIV testing for dental providers; 3. Develop and program the TM intervention, including content, and TM user and interactivity features to increase user appeal and engagement, by conducting qualitative interviews with dental patients (N=32); 4. Conduct pilot testing of rapid HIV testing (n=1 CHC) and referral for HIV testing (n=1 CHC); 5. Conduct pilot testing of the TM intervention among dental clinic patients (N=20). The UH3 Specific Aims are: 1.Conduct a cluster randomized trial among four CHC dental clinics to determine the efficacy of on-site rapid HIV testing in increasing HIV testing rates compared to referral within the CHC; 2. Determine changes in the dental clinic HIV testing rates over time to assess intervention sustainability; 3.Conduct a randomized clinical trial among dental clinic patients (N=266) at increased risk of HIV infection to determine if the dental clinic-delivered TM increases utilization of HIV prevention services including repeat HIV testing, PrEP uptake, and HIV risk reduction compared to a contr...