Project Summary/Abstract Latino children have worse health than non-Latino White children across many common conditions, including respiratory illnesses and obesity, laying a foundation for health disparities across the life course. Prior studies demonstrate that attachment-based parenting interventions, those designed to foster sensitive parenting behavior and secure infant-parent attachment, improve maternal sensitivity, attachment security, child socioemotional development, and some aspects of child psychophysiological regulation. To date, there has not been a large-scale trial testing the efficacy of an attachment-based intervention for supporting physical health more broadly. This is a significant gap, especially with regard to Latino child health promotion, given (a) the promise of attachment-based interventions, and (b) the early origins of health disparities that negatively impact Latino children, the largest and fastest-growing segment of the U.S. population. The proposed RCT will test the impacts of an attachment-based intervention on emerging health outcomes in low-income Latino children (N = 260). We will focus on low-income Latino families as a group at exceptionally high risk for health problems. The manualized intervention, Attachment and Biobehavioral Catch-up (ABC), consists of 10 sessions provided by a trained parent coach to primary caregivers and their infants in their homes. We will enroll families with 9-month-old infants and follow them longitudinally until age 2. In Aim 1, we will test the effects of ABC on child health outcomes. We hypothesize positive intervention effects on common infant and toddler illnesses (e.g., respiratory illnesses), low-grade inflammation, BMI, and sleep. In Aim 2, we will test mediators of intervention effects. We hypothesize (a) positive intervention effects on sensitive parenting behaviors and child stress regulation, and (b) that these factors will mediate intervention effects on child health outcomes. In Aim 3, we will test sociocultural context as a moderator of intervention effects. We hypothesize stronger intervention effects in higher-risk dyads (i.e., mothers who are more acculturated, who have fewer supports, or who experience more discrimination) than in lower-risk dyads. Our proposal is innovative in that the RCT design provides an unprecedented opportunity to test causal impacts of an attachment-based intervention on a comprehensive set of early health outcomes known to track across the life course. This proposal is significant in that it aligns directly with the NICHD priority of Understanding Social Determinants of Health and Developmentally Informed Strategies to Mitigate Health Disparities. We will (a) examine how attachment-based intervention supports a foundation for health and (b) identify subgroups to prioritize in future efforts to optimize health in low-income Latino children.