Ending the HIV epidemic will require dramatically expanding the reach of biomedical prevention tools to populations needing them most. Despite the availability and effectiveness of prevention approaches including pre- and post- exposure prophylaxis (PrEP, PEP) and treatment as prevention, regions of the United States (e.g., South Florida) and key populations continue to experience high HIV incidence. Therefore, the need is urgent for contextually relevant and effective implementation strategies to enhance the reach of evidence-based HIV prevention tools across the prevention cascade for populations that are currently not reached. Accordingly, our team used community engaged methods to develop a prototype for one such implementation strategy – the JUNTOS (Joining Under-connected Networks To Optimize Salud) Referral Network – to improve the reach of PrEP, PEP, and rapid antiretroviral treatment. The implementation strategy seeks to improve reach by (a) improving implementers' ability to navigate clients to PrEP, PEP, and rapid treatment; and (b) increasing demand from potential recipients for services. Our planning work to develop JUNTOS was funded by a federal Ending the HIV Epidemic supplement and included academic (University of Miami, Northwestern University), implementation (Florida Department of Health, Care Resource), and community partners (Community Advisory Board). The next logical step is to develop JUNTOS fully and conduct our proposed type III hybrid effectiveness-implementation trial, with the following aims. Aim 1: Evaluate, at the HIV test counselor level, the implementation outcomes associated with the JUNTOS Referral Network. We will recruit and randomize South Florida HIV test counselors (N=45) 2:1 to either receive JUNTOS or the non-tailored referral list that HIV test counselors currently use (control). JUNTOS recipients will receive training to use JUNTOS for referring their testing clients. We will then evaluate implementation and maintenance, and explore hypothesized mechanisms (e.g., knowledge, network), and also assess acceptability, appropriateness, and feasibility. Aim 2: Evaluate implementation and effectiveness outcomes, at the recipient level, associated with the JUNTOS Referral Network. We will track the extent to which testing clients served by Aim 1 test counselors are reached by evidence-based HIV prevention and treatment services. Up to 5 testing clients per HIV test counselor in the trial will complete brief assessments to evaluate the reach of PrEP, PEP, and rapid treatment before and after their testing session. We will explore differences in PrEP, PEP, and rapid treatment reach between testing clients seen by HIV test counselors in the two arms of the pilot trial and will also explore effectiveness outcomes. Completing this R34 will provide data on JUNTOS' acceptability, appropriateness, and feasibility, and preliminary data on the degree to which JUNTOS is an evidence-based implementation strategy, informing...