We have the biomedical tools necessary to prevent HIV and improve the health of people living with HIV, yet achievement of the Ending the HIV Epidemic goals requires sociostructural interventions that address social determinants of health that contribute to inequities. Evidence-based sociostructural interventions exist that have a direct impact on PrEP, care-related, and viral suppression outcomes, yet they have been much less studied than individual-level interventions and their implementation poses unique methodological and institutional challenges. Determining how sociostructural interventions can reduce health inequities, including implications for implementation and sustainment, is an urgent public health research priority. The Sociostructural Implementation Science Coordination Initiative (SISCI) hub will bring the best of Dissemination and Implementation (D&I) Science to collaborate with the Companion R01s to coordinate data harmonization, foster opportunities for cross-site learning, and coordinate research, capacity building, and dissemination efforts. We will grow the capacity of both researchers and implementers to apply D&I models and methods for developing, testing, and implementing sociostructural interventions. SISCI investigators and consultative team are nationally recognized experts in HIV D&I science and have a strong record of coordinating HIV D&I projects and providing tools and training to the field. The SISCI aims to (1) Assist the companion RO1s through collaboration, knowledge sharing, and expert consultation on D&I science and social determinants of health models and methods. We will coordinate in person and virtual communications between companion R01s and provide tailored methodological support to the projects based on collective needs and opportunities. (2) Integrate implementation and effectiveness data across R01 studies to collect cross-project data and perform integrated analyses. Using shared decision making, we will identify common data elements (CDEs) for collections across projects and plan for integrated analyses. We will deploy data coordination infrastructure to collect cross-project data and perform integrated analyses—whenever possible obtaining administrative data to allow new generalizable knowledge beyond what individual projects have studied. We will disseminate findings on implementation determinants and strategies using our popular HIV implementation science website and newsletter, conference presentations, and a special journal issue of Companion R01 and other sociostructural project findings. (3) Advance the field of sociostructural interventions to reduce HIV disparities by developing and offering a combined D&I science and sociostructural training tailored to early career investigators and implementation partners. We will further grow the capacity of the field by conducting a scoping review to build a compendium of promising and proven implementation strategies for sociostructural interventions....