PROJECT SUMMARY Social isolation is the objective lack of (or limited) social contact with others. Approximately 1 in 4 older adults are socially isolated. Social isolation is a major public health issue and a risk factor for morbidity and mortality comparable to smoking, hypertension, and a sedentary lifestyle. Socially isolated older adults cost Medicare an estimated additional $6.7 billion each year. Low income older adults have two times the odds of experiencing social isolation compared to those with higher incomes. Amidst current aging projections and reports that the current cohort of older Americans have high debt and insufficient savings, the demand for subsidized housing has increased. Few studies examine social isolation among low income older adults living in subsidized housing. Despite epidemiologic evidence demonstrating the deleterious effects of social isolation on health, gaps exist in our knowledge regarding the best solutions to identify and address this major public health problem. This K23 proposal builds upon the candidates’ work funded by the Grants for Early Medical/Surgical Subspecialists’ Transitioning to Aging Research (GEMSSTAR, R03) to advance our understanding of the facilitators and barriers of social isolation among older adults living in subsidized housing. Leveraging these insights, this K23 proposal, guided by the NIH Stage Model for Behavioral Intervention Development, will conduct basic research (NIH Stage 0) to characterize social isolation and its relationship with individual and structural factors among older adults living in subsidized housing to identify participant characteristics that will inform the development of an intervention. These findings will inform the creation (NIH Stage 1A) and piloting (NIH Stage 1B) of a housing-based social isolation intervention pilot. This innovative proposal employs a transdisciplinary approach and builds the foundation for novel approaches to identify and address social isolation among older living in subsidized housing. This proposal will support the research and career development of the candidate, who aims to become an independent clinician investigator focused on developing and implementing community-based interventions that improve the health of low-income older adults.