Infants learn language through the back-and-forth interactions with their parents where they “serve” by vocalizing, gesturing, or looking and parents “return” in a temporally and semantically contingent way. My dissertation focuses on these “serve and return” (SR) interactions between 9-month-old infants and their mothers and fathers (n = 296 parents and 148 infants) from ethnically and socioeconomically diverse backgrounds by examining the variability in SR interactions explained by maternal and paternal psychological distress, the association between SR interactions and children’s language skills at 18, 24, and 30 months, and the moderation effect of maternal and paternal SR interactions on language outcomes. Psychological distress was indicated by parent-reported depressive symptoms, parenting stress, and role overload, and SR interactions were transcribed and coded from video-taped parent-child toy play activities during home visits. I report three major findings. First, neither maternal nor paternal psychological distress was significantly associated with and SR interactions at 9 months, controlling for demographic factors. Second, fathers who responded to their child’s serves more promptly and mothers who provided more semantically relevant responses had children with higher receptive and expressive language skills, respectively, at 18 and 30 months. Third, fathers’ semantically relevant responses were negatively associated with children’s receptive language skills at 24 months; however, this main effect was moderated by mothers’ semantically relevant responses. Understanding how mothers and fathers engage in temporally and semantically contingent social interactions with their children during the first year, especially among families from diverse backgrounds, would enable programs and policies to more effectively promote early language development and reduce gaps in school readiness.