Alzheimer’s Disease and related dementias (ADRD) disproportionately affect individuals from socially disadvantaged groups, but the role of lifespan psychosocial stressors in these disparities is uncertain. Social networks are hypothesized to be key sources of resilience against psychosocial stressors, but it is unknown if they moderate the adverse effects of stressors on ADRD risk or whether the buffering provided by social networks is consistent across diverse racial/ethnic groups. Sleep disturbance is a potential biobehavioral mechanism via which stressors may increase ADRD risk, but the mediating role of sleep has not been formally evaluated. Understanding the effects of psychosocial stressors and modifiable sources of resilience and biobehavioral mechanisms on ADRD risk will guide potential interventions to reduce ADRD disparities. This proposal encompasses a training and research plan to develop the candidate’s expertise in ADRD research, preparing her to launch a career focused on reducing social inequalities in ADRD. The research proposal applies causal inference methods to elucidate the complex relationships between early social disadvantages, psychosocial and biobehavioral factors, and cognitive outcomes in older adulthood. The specific aims are to determine the roles of social networks and sleep disturbances for the adverse effects of early-life stressors on ADRD risk across four racial/ethnic groups. This research will use data from the Kaiser Healthy Aging and Diverse Life Experience Study (KHANDLE), a life-course study linking risk factor data collected in mid-life (40-50 years ago) with contemporary assessments of risk factors, cognitive decline, and dementia in a sample of older non-Latino Whites, Blacks, Asians, and Latinos in California. The proposed project will generate new knowledge and provide crucial training for the candidate’s advancement to become an independent epidemiologist focused on ADRD disparities by developing expertise in 1) causal inference methods, including mediation modeling; 2) the epidemiology of ADRD and quantitative ADRD research methods, including longitudinal analyses and psychometrics; 3) the physiology and psychology of sleep disturbances; and 4) professional skills for an academic research career. The advanced training, mentorship, and protected time provided by this award will provide the candidate with the skills and experience necessary to lead the highest quality aging research and succeed as an independent investigator.