This K01 Mentored Research Scientist Development Award application will facilitate Dr. Laura Beres’ career development as a leading, productive, independent researcher conducting innovative implementation science to maximize the real-world impact of HIV prevention interventions among high-risk populations in low-resource settings. The proposed training plan and research implementation in Zambia will allow Dr. Beres to meet her training objectives, developing the critical knowledge, skills, and competencies required to transition into an independent researcher. She will: 1. Gain expertise in pre-exposure prophylaxis (PrEP) and prevention interventions, 2. Develop skills in evidence-based, stakeholder-informed implementation strategy specification to optimize population-level impact of novel interventions, 3. Develop statistical expertise in discrete choice experiments and latent class analysis, 4. Establish capacity in internet-based recruitment and data collection in a low-resource setting, 5. Understand and measure developmental differences, including cognitive and affective development, among adolescents and young adults and their associations with HIV prevention. Dr. Beres’ mentoring team will support her successful achievement of her training, research, and career development goals. Dr. Chris Beyrer, her primary mentor, is an international expert in HIV prevention. She has five co-mentors: Dr. Sinead Delany-Moretlwe, an expert in LAI CAB as protocol chair of HPTN 084; Dr. Sheree Schwartz, a leading HIV implementation scientist with latent class analysis expertise; Dr. John F.P. Bridges, an international expert in discrete choice experiments; Dr. Julie Denison, an expert in adolescent and young adult development and HIV in Zambia; and Dr. Izukanji Sikazwe, a leading HIV researcher and Chief Executive Officer of Dr. Beres’ collaborating institution, the Centre for Infectious Disease Research in Zambia (CIDRZ). Her Scientific Advisor Dr. Smisha Agarwal is an expert in internet-based research in low-income settings. LAI CAB PrEP was found superior to daily oral PrEP in clinical trials and received US FDA approval in December 2021 with international regulatory approvals pending. LAI CAB PrEP has the potential to prevent HIV among those who experience barriers to effective oral PrEP use, including adolescents and young adults (AYA) in sub-Saharan Africa who remain at highest risk of HIV incidence. The proposed K01 research utilizes implementation science to establish evidence needed to optimize LAI CAB PrEP implementation for AYA in Zambia, minimizing the time from proven LAI CAB PrEP efficacy to population impact: Aim 1. Assess the fidelity and sustainability of implementation strategies for two related interventions: oral PrEP and injectable contraception, to inform LAI CAB implementation using participatory process mapping; Aim 2. Identify preferences for LAI CAB implementation and heterogeneity among AYA and healthcare workers using discrete ch...