PROJECT SUMMARY / ABSTRACT Alzheimer’s Disease (AD), the sixth leading cause of death in the US, is the most common form of dementia in later life. Substantial heterogeneity in the course of disease progression, AD prevalence, and mortality exist by gender and race. Yet, variations in the distribution and the relative importance of risk factors, such as multimorbidity, that may inform gender and racial differences in AD risk and cognitive change over time are not well understood. Data-driven strategies capturing the dynamic nature of chronic disease accumulation may offer critical insight regarding differences in dementia risk and cognitive functioning by gender and race. Further, a robust literature hypothesizes linkages between psychosocial resilience and stress with dementia risk and cognitive functioning. However, the extent to which these factors enhance or attenuate dementia risk and poor cognitive functioning merits systematic investigation and is in alignment with new priorities for AD and aging research. To address these gaps the proposed work will investigate the association between multimorbidity trajectories, psychosocial resilience/stress, dementia risk and changes in cognitive functioning using data from the Health Retirement Study (2000-2018). We propose two aims: 1) assess the effect of psychosocial resilience (e.g., perceived social support, self-efficacy, and mastery) on the relationship between multimorbidity trajectories and change in cognitive functioning and incident dementia; and 2) assess the effect of psychosocial stress (e.g., discrimination, chronic stress, social isolation) on the relationship between multimorbidity trajectories and change in cognitive functioning and incident dementia. Specifying multimorbidity trajectory classes that differentially predict dementia risk and poor cognitive functioning represents a valuable contribution in: clarifying factors that propagate gender and racial disparities in late life progressive cognitive decline and dementia risk; informing the design of interventions and preventive strategies targeting psychosocial resilience and stress among populations at greatest risk; and improving precision in stratifying risk for poor cognitive function to delay the development and progression of AD.