PROJECT SUMMARY/ABSTRACT Beyond the role that individual factors (e.g. age, race, gender, and socioeconomic status) play in the progression of Alzheimer's Disease and related dementias (ADRD), neighborhood factors (e.g. social and built environments) may affect cognitive health. Critically, although African American and Hispanic individuals face the highest and most disproportionate risk for ADRD, research has traditionally excluded diverse populations. Given historic and current patterning of healthy neighborhood factors by racial and socioeconomic characteristics, these features may partially explain observed disparities in ADRD risk. To date there has been no research on the role of neighborhood environments in disparities in ADRD risk. In this study, we propose to leverage and extend extensive longitudinal data from the Multi-Ethnic Study of Atherosclerosis (MESA) to address major gaps in research on neighborhoods and disparities in ADRD. We propose to undertake large-scale collection, processing, and distribution of new neighborhood data within MESA. Our main objective is to identify unique patterns of neighborhood change related to the causes of prevalence and disparities in cognitive decline and dementia. We will attain our main objective by (Aim 1) characterizing dynamic, longitudinal neighborhood social and built environment variables (survey-based and GIS-derived) relevant to cognition for residential addresses of a MESA; (Aim 2) examining associations of neighborhood environmental characteristics with cognition and clinically relevant ADRD outcomes; (Aim 3) investigate determinants of disparities in ADRD outcomes by socioeconomic position and race/ethnicity and assess the contribution of neighborhood environments. This project is poised to provide robust new evidence about pathways and links between neighborhood environments and cognitive outcomes, with important implications for built environment science, ADRD progression research, and policies to support healthy aging. Aim 1 will create the most comprehensive longitudinal neighborhood dataset on a diverse sample with detailed cognitive and ADRD outcomes for widespread dissemination to a network of researchers. Analyses in Aim 2 will contribute to developing substantive theory on the role of neighborhoods in ADRD progression and provide guidance for urban planners to design neighborhoods that support healthy aging. Aim 3 examines component contributions to racial disparities in cognition and ADRD. Through this, we expect to identify actionable, community and clinical interventions to address and remediate racial and socioeconomic inequalities derived from the unequal distribution of environmental supports for healthy aging. We expect this evidence to support and amplify efforts to reduce disparities.