The scale-up of global antiretroviral therapy (ART) represents an unparalleled global health success story, leading to impressive overall reductions in HIV-related morbidity and mortality. However, adolescents and young adults (AYA), especially those in Sub-Saharan Africa, have largely been left out of this story. While AIDS-related deaths declined by 30% for adults from 2005-2012, they increased by 50% among AYA over the same period, making AIDS the leading cause of death among African youth. AYA living with HIV perform poorly across the entire care continuum. ART adherence is central to effective HIV treatment, but AYA have high rates of virologic failure, virologic rebound after initial suppression, and attrition from HIV care. Unique developmental features of adolescence and young adulthood such as impulsivity, risk-taking, and poor concrete thinking make daily medication adherence even more challenging in this population. In addition, the attitudes and behaviors of young people are often strongly influenced by their peers. This influence can be seen as a powerful incentive for desired behaviors. Much of the literature has focused on financial incentives, which have shown success in promoting health behaviors. There are few data exploring mobile health (mHealth) technologies to exploit social and financial incentives, yet mHealth platforms allow for the delivery of novel behavioral interventions. With the proliferation of mobile phone ownership in Sub-Saharan Africa in general and in Nigeria in particular, such interventions can be delivered where there is greatest need. More than 75% of HIV-infected AYA live in Sub-Saharan Africa, and fully 10% reside in Nigeria. In this proposal, we will adapt an mHealth application, PEERNaija, to leverage both social and financial incentives to improve medication adherence among AYA living with HIV in Nigeria. We will also work with our partners at APIN Public Health in Nigeria to improve capacity to conduct independent mHealth research. The PEERNaija application will feature routine medication reminders, along with individual adherence monitoring with adherence scores, anonymized peer adherence scores (from peers attending the same clinic; social incentive), and a monthly lottery-based prize for youth with the highest adherence scores (financial incentive). To accomplish these aims, we will build on previous collaborations between Vanderbilt and APIN, a multi-site PEPFAR-supported program serving more than 250,000 persons living with HIV in Nigeria. We will engage key stakeholders in the community through focus groups and key informant interviews to guide iterative adaptation of the app. We will recruit a cohort of 50 HIV-infected AYA to pilot the app and assess feasibility, acceptability, adoption, and preliminary efficacy of important clinical measures (including adherence and virologic suppression). The proposed study will provide important preliminary data for the role of mHealth platforms to harness and deliver social and financial incentives to promote adherence efforts, especially for vulnerable youth, and for a larger intervention trial evaluating this app among HIV-infected AYA in Nigeria.