PROJECT ABSTRACT Prevention of mother-to-child transmission (PMTCT) efforts have reduced the rates of vertical transmission to 2.7%, however, optimal antiretroviral therapy (ART) adherence remains a difficult goal to reach, particularly postpartum. The contribution of the proposed research is expected to be two-fold: 1) to gain an understanding of how influential contextual, interpersonal, clinic, and individual level factors change during key moments of transition during pregnancy and postpartum and influence ART adherence and 2) to develop bio-behavioral interventions to assist mothers in maintaining their adherence to ART postpartum. Candidate: I am a social psychologist with a background in ART adherence among socially disadvantaged groups in the United States. This five-year K01 Career Development Award has been used to obtain training, mentorship, and research experience to become an expert in maternal health among women living with HIV in resource limited settings and an independent investigator capable of obtaining R01 funding. Research: The goals of the proposed project are to (1) identify contextual, interpersonal, clinic, and individual level factors that influence women’s HIV treatment adherence during key periods of transition during pregnancy and postpartum; (2) evaluate a Transition Theory-based bio-behavioral intervention to improve ART adherence postpartum using a small scale randomized controlled trial; (3) assess participants’ experiences of the intervention, perceived usefulness, and identify ways to refine the intervention for future evaluation. Administrative Supplement: The purpose of this administrative supplement is to provide additional support to offset the impacts of the COVID-19 pandemic on the research originally proposed. Considerable progress has been made on the training and research associated with this grant, however, due to COVID-19 related delays and restrictions, the completion of Aim 3 is currently in jeopardy of not being completed. The Aim 3 data are critical to my training and future likelihood of success as an independent investigator.