Project Summary/Abstract The goal of this study is to identify early risk for developmental language disorder (DLD) among young, low- income children, and to determine how caregiver and child chronic stress and interaction quality interact to disrupt language growth among these vulnerable children. The study is designed to address disparities in the rate of DLD among young children, with low-income children disproportionately affected (Norbury et al., 2017). The long-term objective is to identify pathways through which early family contexts and the conditions of poverty disrupt early language trajectories among low-income children and contribute to heightened rates of DLD. The proposed longitudinal study addresses three specific aims regarding low-income dyads: (1) to identify whether and to what extent caregiver stress affects their young children’s language trajectories and DLD status at 54 months; (2) to identify the extent to which children’s physiological stress contributes to their early language trajectories and DLD status at 54 months, and determine whether it is a key mediator of caregiver stress on these outcomes; and (3) to determine the interplay among caregiver stress, child stress, and caregiver-child interactions for their effects on children’s early language trajectories and DLD status at 54 months. Study procedures involve ascertainment of 320 low-income mothers and their 6- to 11-month-old children using medical records from a large urban hospital; eligible dyads will reside in households at or below 200% of the federal poverty level. Measurements are collected thrice annually (one study visit, two in vivo observations) to comprehensively map family processes and experiences, caregiver-child interaction quality, caregiver stress and stress physiology, child stress physiology, and children’s linguistic trajectories until 54 months. The initial two study aims are addressed using multi-level growth models, with caregiver and child stress, respectively, as time-varying predictors. The third study aim uses multilevel path analyses to examine the interplay among child and caregiver stress, caregiver-child interactions, and children’s language trajectories and DLD status at 54 months.