ABSTRACT – METHODS CORE The Methods Core supports the CHIPTS mission by guiding measurement, statistical methods, and implementation science across the center's aims and initiatives, maximizing innovation and impact. It applies methods expertise specifically toward assessing influences of mental health, substance use, and social and structural determinants of health on HIV-associated treatment and prevention outcomes. We respond to an HIV research environment with an expanding mix of biomedical strategies, including long-acting agents for HIV prevention and treatment, as well as a growing need to integrate information from multiple data sources (e.g. mobile-phone-based assessments, electronic health records, laboratory data, administrative and public-use databases). The push toward implementation science, community-partnered research, and team science demands development of new methods. The Methods Core also targets measurement and evaluation of persistent disparities across diverse racial/ethnic and sexual/gender minority populations in advancing HIV research methodology when conducting investigator-initiated research and service-oriented activities. The specific aims are (1) Science: To foster and facilitate cutting-edge HIV research by developing and disseminating innovative technologies and analytic strategies for combination HIV prevention and treatment research that transcends individual models, including but not limited to implementation science; (2) Networking: To connect scientists across disciplines and across networks with complementary expertise and community partners to bi-directionally inform available research tools and identify need for advances in analytic methodologies; and (3) Capacity building: To recruit, mentor, and support high-caliber investigators with methods expertise and disseminate innovative methods, assessment tools, and platforms through in-person and virtual training activities with emphasis to emerging scientists from underrepresented minorities in science. The Methods Core is guided by a broad causal-inference paradigm to maintain a scientific foundation in all research activities and in evaluating potential impacts. The Methods Core will prioritize three areas: (a) Harmonizing evidence across multiple data sources; (b) Statistical methods for complex applied contexts including management of high-dimensional measurements, of varying data types, of missing data, and of other complexities in HIV prevention research; (c) Dissemination and implementation science consultations utilizing participatory approaches, balancing fidelity and adaptation, identifying core elements, modeling decision- making in intervention adoption, and applying system-analytical tools. In housing the “UCLA Rapid, Rigorous, Relevant Implementation Science Hub”, the core further expands its capacity to support and guide implementation science principles and best practices in HIV prevention.