Project Abstract/Summary Externalizing behaviors in childhood are detrimental to building prosocial connections, achieving academically, and maintaining positive mental health. Therefore, it is crucial to identify factors that increase children’s risk for externalizing behaviors. Prenatal chemical exposures (e.g., phthalates, organophosphorus pesticides, lead) have been associated with increased risk for child externalizing behaviors. However, much of this work examines the influence of single chemical exposures, with less research considering the real-life prenatal context of simultaneous exposures to multiple chemicals that could compound risk for child development. Moreover, to a large extent, studies have ignored the importance of genetic risk and gene-environment interplay. Genetically informed designs have the potential to contribute to our understanding of the mechanisms by which prenatal chemicals may influence child behavior. The current proposal will address these gaps in the literature, making use of two existing longitudinal studies of child development, The Mount Sinai Children’s Environmental Health Study, and the Twin Study of Behavioral and Emotional Development – Child. The research goals of this fellowship are: (1) Using a person-centered, Latent Profile analytic approach, to examine how patterns of prenatal chemical exposures increase risk for externalizing behaviors in a longitudinal multiethnic cohort of pregnant women, and (2) Using a genetically informed design, to examine how prenatal chemical exposure moderates the etiology of child externalizing behaviors in a disadvantaged twin sample. The interdisciplinary approach of this proposed fellowship will refine a conceptual model that integrates genetic and prenatal environmental influences on child externalizing behaviors. The proposed fellowship will provide additional training to: (1) gain experience in environmental epidemiology, (2) gain experience in exposure mixture modeling, (3) develop an integrated conceptual model of the ways in which the prenatal environment moderates genetic and environmental influences on child social development, (4) strengthen networking, research dissemination, and grant writing skills, and (5) obtain additional training in the responsible conduct of research. This fellowship will augment my existing training in social contexts for child behavioral development with focused research and training in environmental epidemiology and behavioral genetics. Therefore, this work will support my career goal of becoming an independent researcher at the intersection of multiple fields crucial to the understanding of child behavioral development (developmental psychology, environmental epidemiology, and behavioral genetics).