Developmental neuroscience and psychopathology have great potential to inform the understanding of the causal pathways and mechanisms of mental illness. This T32, which is focused on this domain, is co-led by Drs. Luby and Barch (with complimentary expertise in developmental psychopathology and neuroscience), and has been very successful in the first two cycles of funding, enjoying a highly competitive national applicant pool and successfully launching the young scientists completing the program into research careers and external funding. We seek to renew this training grant, adding new expertise in a wider range of neuroimaging measures, as well as new faculty mentors with expertise in the effects of genetics, the gut microbiome, and sleep/circadian rhythms on neurodevelopment and risk for psychopathology. From a public health perspective, an infusion of new research scientists in the area of developmental neuroscience and psychopathology continues to be a high priority. The proposed multi-disciplinary training approach is guided by a conceptual model that recognizes that the risk, onset, and course of psychiatric disorders arises through a complex interplay of brain developmental processes influenced by environmental, psychosocial, cognitive, affective, genetic, and biological factors that interact beginning in utero and continue throughout development. Numerous investigators at Washington University in St. Louis (WUSTL) have a rich track record of experience in many aspects of child neuroimaging and related methods, including a focus on structural and functional magnetic resonance approaches in very early childhood (including neonates), functional near-infrared spectroscopy (fNIRS), evoked response potentials (ERP) and high density diffuse optical tomography (HD- DOT). Further, WUSTL has an international reputation in psychiatric genetics, gut microbiome work, and sleep/circadian rhythms, with many researchers who can bring their expertise to bear on understanding the neurobiology of developmental psychopathology. The program mentors have a rich body of available databases derived from longitudinal studies, several of which began in early childhood and in utero. Mentors also provide a unique multidisciplinary training environment in which to pursue this exciting domain focused on development, given the established collaborations between child researchers in the WUSTL School of Medicine clinical and basic departments, and the state of the program in neuroscience and neuroimaging at WUSTL that has been at the forefront of developmental cognitive and affective neuroscience. Interactions between researchers in basic and clinical developmental neuroscience offer an ongoing opportunity to help train the next generation of young scientists who can pursue questions about the developmental etiology of psychopathology from the perspective of core psychological and neural mechanisms of human behavior that span traditional boundaries of psychopathology, a...