Project Summary/Abstract Women’s exposure to early life stress (ELS) can have lasting adverse consequences for emotional, cognitive, and biological functioning that extend into their child-bearing years. Emerging research suggests that the negative effects of ELS can be transmitted across generations, beginning in the prenatal period. In this project, we posit that mothers’ exposure to stress during their own childhood affects the neurodevelopment of their offspring, first, by influencing the intrauterine endocrine milieu and, subsequently, through the process of dyadic physiological synchrony. Specifically, we posit that early exposure to life stress affects the pre- conception setpoint for the hypothalamic-pituitary-adrenal (HPA) axis, disrupting maternal levels and trajectories of cortisol across pregnancy and altering fetal neurodevelopment. We posit further that in the postnatal period infants continue to be affected by maternal HPA-axis dysregulation through concordance of their own HPA-axis functioning with that of their mothers. In this application, we propose conduct secondary analysis of banked samples of women’s hair obtained at three time-points: at mid-pregnancy, approximately 1 month after birth, and at infant age 6 months. From these samples, we will derive monthly levels of cortisol production across pregnancy and the early postnatal period, enabling us to examine the effects of maternal exposure to ELS on levels and trajectories of maternal hair cortisol concentration in the perinatal period and the effects of this cortisol production on both their infants’ hair cortisol concentration and their infants’ hippocampus and amygdala volume at age 6 months. This project promises to yield critical and specific insights, informing our understanding of maternal factors that affect child neurodevelopment.