PROJECT SUMMARY Sleep deprivation in American youth and young adults is a major public health problem and can impair mental and physical health, cognitive functioning and stress response systems. Significant gaps in this research include scarce investigations of long- term developmental trajectories of adaptation and maladaptation associated with sleep disturbances in the context of socioeconomic and racial/ethnic disparities. Identifying mechanisms that explain SES and racial disparities in sleep and broader health outcomes, as well as factors that prevent or protect against broader health disparities are high scientific priorities (Healthy People 2030). The proposed study addresses these gaps and advances parent grant discoveries. The design builds on a well-characterized two-wave study with adolescents (16-19 years; n=300) and involves two additional waves with young adults (~ 21-24 years; target n=300); analyses will also capitalize on existing data for a subsample (n=199) who participated during childhood (9,10,11 years). The sample consists of young adults from semi- rural Alabama; 54% women; high representation of Black participants (39%) and socioeconomic adversity. This sample is unique, underrepresented in the literature, and ideal for testing the research questions. Strengths of the design include the large and diverse sample, high retention rates, breadth and rigor of measurement across important outcome domains, a four-wave design spanning adolescence and young adulthood, a large subsample with three additional waves in childhood, and analyses of long-term trajectories of mental and physical health, cognitive functioning and autonomic nervous system activity. Towards scientific rigor and reproducibility, well-established procedures, questionnaires, hardware and software will be used. Sleep is examined objectively with actigraphy and subjectively. Comparable long-term investigations of health disparities utilizing objectively-assessed sleep and developmental trajectories of multiple health domains in such a sample do not exist. The study will advance understanding of the long-term effects of sleep across development in the context of socioeconomic and racial health disparities by identifying the role of sleep in transmitting risk or functioning as a vulnerability or protective factor. Study goals are consistent with the strategic goals and high-priority research areas of the 2021 NIH Sleep Research Plan including advancing understanding of sleep’s contributions to health disparities in socioeconomically disadvantaged and minoritized groups. Findings will help identify individuals at greatest risk for negative health outcomes and identify behavioral and ecological targets for prevention and intervention.