DESCRIPTION (provided by applicant): The prevention science is increasingly clear: biomedical interventions hold great promise to prolong life and decrease both infectiousness (of those living with HIV) and susceptibility (for those who are HIV-negative and take pre-exposure prophylaxis [PrEP]). However, these strategies do not stand alone; it is equally clear that combinations of behavior change and biomedical interventions work together to reduce new HIV infections for MSM. Biomedical tools will not have sufficient impact unless they are combined with increased HIV testing frequency, paired with coordinated behavior change interventions, integrated within communities, and brought to scale. We propose develop a new set of HIV prevention messages based on rigorous preliminary qualitative studies, and reflecting the current age of combination biomedical and behavioral prevention. We will use mobile technology to test the messages, and to provide links between targeted prevention services and service access points in Atlanta, Detroit, and New York. The prevention app through which the new messages will be tested has already been developed, building on a mixed-methods formative research process that incorporated the input of academics, community-based organizations, and health departments. The content of the new messages will be guided by Social Cognitive Theory. Once developed, the new messages will be tested in a delayed-onset design among 1206 MSM, stratified by HIV status (HIV-positive and HIV negative) and, within HIV-negative men, by risk (lower risk and high risk). Outcomes will be self-reported HIV prevention and risk outcomes, assessed at the end of a 3-month intervention period. The study team is well prepared to conduct the proposed activities, having enrolled >100,000 MSM in HIV prevention studies, having enrolled >20,000 MSM in 11 RCTs of HIV prevention research, and having develop multiple mobile applications for HIV prevention and research with MSM.