There is compelling evidence for a critical role of the maternal and infant gut microbiome in early infant brain neurodevelopment. Temporal milestones in postnatal infant gut microbiome development align with changes in early infant brain development, suggesting functional relationships between these two pivotal events. The premise of our proposal is based on a wealth of studies and new preliminary analyses reported below linking maternal prenatal anxiety (PNA), a prominent prenatal maternal risk factor, and child neurodevelopment. We hypothesize that the prenatal maternal microbiome and its influence on newborn neurodevelopment is shaped by PNA, and that early infant cognition is determined by mother-to-infant microbiome transfer, postnatal development and biosynthesis of microbiota-derived neuroactive metabolites (NAMs). Our study is framed by a proposed developmental model that includes two major components; prenatal anxiety and developmental phase trajectories of the infant gut microbiome. The proposed model has scientific as well as practical strengths, as it leverages a wealth of existing data collected as part of a large, prospective longitudinal and diverse pregnancy cohort that has been followed from the first trimester through the child’s 4th year, with extensive longitudinal characterization of prenatal exposures, child microbiome and other key biological samples, and child neurodevelopment assessed longitudinally that will enable important and previously neglected incorporation of potential confounds. We use these components to test the central hypothesis that neurodevelopment is dependent on age-driven biosynthesis of NAMs through the postnatal period of infant gut-microbiome (IGM) development. In Aim 1, we use metagenomic analysis of the prenatal maternal vaginal microbiome (MVM) to identify species and functional biosynthetic pathways for NAMs associated with PNA. We also assess the potential transfer of maternal anxiety through the initial colonization of the infant gut microbiome by an anxiety “imprinted” MVM. In Aim 2, we use metagenomic and metabolomic analyses to determine the association between key stages of IGM development and differential synthesis of NAMs over the first year, attending to confounds and competing exposures, most notably, maternal diet and infant feeding. In Aim 3, we apply this rich data to predict neurocognitive assessments from age 1 to 4 years to formally test the temporal relationship between microbiome phase and neurodevelopment in the first year of life and durability of the microbiota- neurodevelopment relationship through 4 years of age. The scientific impact of the study will be on advanced understanding of the role of prenatal exposures; documenting sources of between- and within-individual differences in the IGM through the first years of life; identifying NAMs with a possible mechanistic role in the MGB axis; documenting a potentially broad and persistent impact on neurodevelopment.