The proposed study will assess implementation of an evidence-based Integrative HIV-SMI Case Management (IHSCM) approach to care integration for people with HIV and serious mental illness (SMI) in a Ryan White Part A (RWPA) setting in New York City (NYC). Lacking an integrated system of care for chronic, co-morbid, intensive- need conditions, people with SMI and HIV—whose rates of HIV infection are 4-10 times higher than the general population’s—are among the highest service utilizers across multiple care systems yet have among the worst HIV health outcomes. Guided by our Implementation Research Logic Model based on the Consolidated Framework for Implementation Research (CFIR) and Expert Recommendations for Implementing Change, our specific aims are to: 1) Utilize CFIR to identify current practices, gaps, disparities, barriers, and facilitators to implement IHSCM for integration of care for HIV and SMI in one RWPA setting; 2) Tailor implementation strategies to conditions identified in Aim 1; 3) Implement strategies tailored in Aim 2, and collect and analyze interview and survey data to assess outcomes aligned to the Outcomes Crosswalk: acceptability, appropriateness, feasibility, equity, and patient-centeredness; and 4) Use findings from Aims 1-3 to determine applicability of IHSCM strategies across other jurisdictions to inform future large-scale implementation. Our goal is to develop locally defined strategies for integrating care for people with two chronic, comorbid, intensive-need conditions to achieve improved health outcomes and secondary prevention. Building on our prior HIV-behavioral health care integration planning supplement, which successfully coalesced diverse system settings and jurisdictions to inform directions for new implementation research, and using a mixed methods design, we will evaluate the implementation of IHSCM in a RWPA setting in NYC, with potential to be scaled up by the New York City Department of Health and Mental Hygiene and RWPA settings across NYC to improve HIV outcomes and reduce health disparities in a NYC EHE priority population. This study addresses two pillars of the federal EHE Plan, Treat and Prevent, as well as key NIH HIV/AIDS high-priority research areas: 1) Address HIV co- morbidities through research designed to manage these conditions; and 2) Advance Cross-Cutting Areas of research in the behavioral and social sciences, epidemiology, implementation science, and information dissemination. This project is responsive to the Supplement Announcement in several ways: (1) it is an equity- focused approach that will reduce disparities in HIV treatment and related health outcomes; (2) it addresses a highly stigmatized priority population (people with SMI) as stipulated in the NYC EHE Plan and its Ryan White Planning Council; (3) it builds upon meaningful partnerships across critical government public health, community, research, and implementation organizations in NYC and upon a strong collaboration with on...