Sub-Saharan Africa is most severely affected by the HIV epidemic, particularly Zambia. Young people with HIV (YPWH) are disproportionately impacted by HIV/AIDS. Emerging adulthood (ages 18-24) is characterized by increasing independence, risk-taking behaviors, identity exploration, and changing social supports, which may impact HIV management behaviors, including medication adherence, retention in care, sexual risk behavior, and substance abuse. Substance use has synergistic and additive effects on health and HIV-related comorbidities, and accelerated HIV disease. Self-management interventions targeting HIV and substance use reduction in Zambian YPWH are urgently needed. We propose to develop and pilot a multi-component, mHealth intervention to promote HIV self-management and reduce substance use. We will adapt the 4- session, in-person Healthy Choices (HC) intervention for mHealth (mHC) to increase access and delivery of HC. In addition, we will develop and pilot test Motivational Text Messaging (MTM) to enhance the impact of mHC. mHC and MTM will be delivered using Computerized Intervention Authoring System (CIAS). Our primary aim is to develop and assess the preliminary efficacy of the resulting mHealth intervention. We will utilize a Multiphase Optimization Strategy (MOST) framework to identify the most effective intervention component or combination of components that addresses self-management and substance use among YPWH in Zambia. The proposed study includes 3 phases. Phase I includes focus groups with Zambian YPWH to explore barriers and facilitators of HIV self-management and substance use to inform the intervention. Phase II consists of adapting and beta testing of mHC and MTM for functionality and feasibility using a community advisory board of Zambian YPWH, local healthcare personnel, and community leaders. In Phase III, we will conduct a pilot using the MOST framework to assess feasibility, acceptability, and preliminary efficacy of intervention components (mHC and MTM) to improve HIV self-management and reduce alcohol and other drug use. One hundred YPWH be randomized to four experimental conditions: 1) Standard ART Counseling (SAC), 2) mHC + SAC, 3) MTM + SAC, and 4) mHC + MTM + SAC. Feasibility and acceptability of the intervention will be assessed through paradata of usage patterns and the System Usability Scale. Preliminary impact will be assessed by evaluating ART Adherence and substance use. YPWH will complete assessments at baseline and 3-, and 6-months post-intervention. Biomarkers of adherence to ART and HIV/STI will be collected. Upon project completion, we will have an optimized mHealth intervention to support YPWH’s self- management of HIV which will be ready for testing in a larger efficacy trial.