PROJECT SUMMARY Men who have sex with men (MSM) bear a greater burden of HIV/AIDS than any other population group in the US, comprising only 2% of the population but 56% of individuals living with HIV/AIDS. Although much of the increased incidence in HIV has been reported among young MSM (YMSM), especially among racial and ethnic minority groups, and is linked to high-risk sexual behavior, there remains a dearth of evidence-based HIV prevention interventions for YMSM – and none that address racially/ethnically diverse YMSM. To address this need, our study, in response to RFA-MD-15-012, leverages mobile technology and MyPEEPS, an existing theory-driven, multi-ethnic, group-level, evidence-based intervention for diverse YMSM. MyPEEPS is a manualized curriculum, developed by members of our proposed Investigative team, comprised of 6 modules focusing on key intermediate social and personal factors, including knowledge (e.g., correct way to use a condom), self-efficacy for safer sex, interpersonal communication skills and behavioral skills. MyPEEPS is one of the only HIV prevention interventions in the literature that focuses on diverse adolescent MSM. Long-term sustainability of face-to face, group-level behavioral interventions, such as MyPEEPS, have been problematic for dissemination in at-risk populations, particularly among young racial and ethnic minority groups. In response to this challenge, we propose to translate MyPEEPS from a face-to-face, group-based curriculum to a mobile, responsive-driven web-based platform, accessible by smartphone or other web-enabled devices, to increase accessibility and scalability for diverse YMSM. The ubiquitous nature of mobile phones in daily life, especially among 13-18 year olds, has created opportunities for health interventions in a portable format with enhanced privacy. Using a participatory approach, our study will incorporate user-centered design in the translation of the MyPEEPS intervention onto a mobile platform. MyPEEPS Mobile will be tested in an RCT with racially and ethnically diverse HIV-negative or unknown status YMSM aged 13-18 at four geographically diverse sites: Birmingham, Chicago, New York City, and Seattle, allowing for increased generalizability of findings. The proposed MyPEEPS Mobile intervention is a novel and evidence-driven intervention using mobile technology to deliver HIV prevention information specifically developed for at-risk YMSM. This will be the one of the first studies to test the efficacy of a scaled-up, mobile version of an existing HIV prevention intervention originally developed for, designed by, and piloted for, a diverse group of YMSM. The research team has unique experience and expertise to conduct this important work and has conducted significant preliminary work related to the project goals. If efficacious, the public health impact is large, as the intervention will already be in mobile format which is well-suited for widespread dissemination.