PROJECT SUMMARY/ABSTRACT A number of HIV prevention interventions are known to be effective: HIV testing and linkage to care as appropriate, condom use, and HIV pre-exposure prophylaxis (PrEP). Unfortunately, achieving sufficient use of these prevention services has been challenging. In China, men who have sex with men (MSM) are the only risk group with increasing HIV case detection, representing 26% of new cases diagnosed in 2014. One way to obtain increased prevention intervention use would be to help individuals understand when they should be using certain prevention services, and to make accessing services less burdensome. The proposed research will involve conducting a literature review and developing mathematical models to explore different scenarios of providing a combination HIV prevention service intervention for MSM in China. Using information from this exercise, we will develop and pilot test a combination HIV intervention built into a smartphone app. The intervention will include home care services such as home HIV self-testing and home ordering of prevention products such as condoms. If the intervention proves to be feasible and acceptable, the pilot test will facilitate design of a larger study of intervention efficacy. The intervention will be built into an existing, widely-accessed geosocial networking app used by MSM. By building the intervention into a platform already used by millions of individuals, we anticipate that, in the event that the intervention is demonstrated to be efficacious, scale-up of the intervention will be readily achievable. The proposed research seeks to develop mathematical models and an intervention that would reduce the incidence of HIV/AIDS, meeting an overarching research priority identified in the Strategic Plan of the NIH Office of AIDS Research.