Project Summary/Abstract HIV infection and unintended pregnancy are highly prevalent, life-altering events among adolescent girls and young women in low- and middle-income countries. Due to a number of biological, social, and structural factors, adolescent girls and young women in sub-Saharan Africa remain the sub-population most susceptible to HIV infection. Further, the majority of pregnancies among adolescent girls and young women occur in low- and middle-income countries with the highest rates found in sub-Saharan Africa. In Zambia, female university students are a neglected, high-risk sub-population for both HIV infection and unintended pregnancy. Oral pre- exposure prophylaxis (PrEP) and modern contraception are key biomedical prevention tools but increasing the uptake among young women in sub-Saharan Africa has proven challenging. Based on preliminary research, we propose to design a novel peer navigator PrEP/contraception mhealth intervention targeting high-risk female students at the University of Zambia. The peer-navigator intervention will be facilitated by a tablet-based platform to assess HIV and unintended pregnancy risk, provide education and information, link high-risk young women to sexual and reproductive services, assess preferences for peer support, track the use of health services, and provide ongoing support for PrEP and contraception uptake and persistence through regular communication. Using a mixed methods phased approach guided by integrated behavioral and mHealth theories, we will first adapt an existing app (PEBRA) using Human-Centered Design and qualitative methods to create a new tablet- based app to serve as a platform for peer navigators to promote and track PrEP and contraception use among high-risk female students (Aim 1, R21 phase). After several iterations have been evaluated by stakeholders, we will test the app and peer-navigator intervention package in a small prospective single-arm trial, collecting data on the functionality of the app and the acceptably/appropriateness of the peer-navigator intervention (Aim 2, R21 phase). After refining the app and intervention package, we will then thoroughly test the mHealth intervention through a single-site hybrid type 1 effectiveness-implementation randomized controlled trial to 1) determine the effectiveness of the intervention to increase PrEP use and modern contraceptive use, 2) establish underlying behavioral mechanisms, and 3) evaluate implementation-related factors that will enhance the likelihood for the mHealth intervention to be implemented, sustained, and scaled (Aim 3, R33 phase). If proven effective, the peer- navigator mHealth intervention will provide a scalable model to fill-in persistent gaps in HIV prevention and reproductive health among young women in high HIV prevalence low- and middle-income country settings.