ABSTRACT Sustained retention in HIV care is critical for viral suppression, but people living with HIV (PLWH) frequently transition in and out of care over time, putting them at high risk for ongoing viremia and drug resistance. Even when PLWH return to care after loss to follow-up (LTFU), rates of becoming LTFU again in the future are very high. Our preliminary data from Zambia suggests that 30% become LTFU again within 6 months, and that 50% of those who are currently LTFU have previously cycled in and out of care. The time of reengagement in care is thus a critical period to intervene in this high-risk population, and strategies to improve post-return care delivery are urgently needed to break ongoing cycles of disengagement. After returning to care, PLWH often report being scolded, health care workers (HCW) delay ART re-initiation due to adherence concerns and do not consistently monitor virologic response, and PLWH likely still experience the life situations (e.g., competing obligations, travel away from home, or psychosocial factors) that led to their initial LTFU. Strategies to 1) target HCW behaviors (i.e., welcoming returning patients, prompt ART re-initiation) using implementation strategies such as practice facilitation and audit and feedback and 2) offer PLWH support services tailored to their initial reasons for LTFU (e.g., extended refills, transfer coordination, peer-navigation) may be promising. To be successful, however, we need to understand how to effectively implement these approaches into existing care, including 1) how to engage HCWs in attitude- and behavior-change strategies, 2) what support services to prioritize for different barriers, and 3) how to integrate activities into existing workflows. This R34 proposal will build the necessary foundation for implementing a multicomponent reengagement strategy to support sustained reengagement after returning to HIV care. In Aim 1a, we assess patient and HCW needs and preferences for reengagement strategies with patient semi-structured interviews (n=20) and focus group discussions with HCWs and clinic leadership (4 FGDs, n=8-10 each). In Aim 1b, we conduct discrete choice experiments (200 PLWH, 100 HCWs) to quantify relative preferences for the contents and attributes for our reengagement strategy. In Aim 2, we undertake a human- centered design process that engages key stakeholders (PLWH, HCWs, clinic leadership, Ministry of Health) in co-developing the content and features of a multicomponent reengagement strategy focused on 1) improving the patient reengagement experience, 2) optimizing ART re-initiation and viral load monitoring post-return, and 3) providing tailored services that target individuals’ specific reasons for LTFU. In Aim 3, we will pilot the developed strategy at one urban and one rural clinic in Lusaka, Zambia. We will use a mixed-methods approach to assess the implementation (e.g., acceptability, appropriateness), service delivery (e.g., time to ART re- initia...