Although infant sleep regulation across the first year proceeds well for many infants, for many infants that is not the case, and estimates of sleep problems among infants and preschoolers range between 25%-33%. Dysregulated infant sleep is predictive of poor parent sleep, and chronic sleep disruption can place families in turmoil, with consequences for the marital and coparenting relationship. Further, mothers reporting early coparenting distress are at risk for personal distress and poor bedtime and nighttime parenting, which in turn predicts infant sleep problems and insecure infant attachment. This application proposes a randomized clinical trial (RCT) to evaluate the effects of a sleep-enhanced adaptation of an evidence-based transition-to-parenting coparenting intervention program [Family Foundations - FF). The rationale for this study is twofold. First, recent findings from the PI's Project SIESTA (R01HD052809) indicate that poor coparenting at one month post-partum predicts persistent infant-parent co-sleeping across the first year, elevated maternal depressive symptoms, emotionally unavailable bedtime parenting, and insecure infant-mother attachments. Second, whereas FF as originally developed has been successful in improving coparenting, marital adjustment, and overall parenting quality, it gives little specific attention to coparenting in infant sleep contexts, which SIESTA findings identify as critically important to parent and infant outcomes later in the first year. The proposed 3-arm RCT responds to these concerns. In one arm, families will experience FF as originally formulated; in the second, families will receive an adapted FF that emphasizes coparenting in infant sleep contexts; the third arm will serve as controls. Assessments of coparenting and parenting in infant sleep contexts, parental adjustment to infant sleep behavior, choices about sleep arrangements, infant and parent sleep quality, and infant socio-emotional functioning, will serve as outcomes. Our central hypotheses are: (1) Compared to controls, parents in both FF groups will report improved overall coparenting and reduced overall distress, but parents in the adapted FF group will show greater improvements in coparenting and individual parenting in infant sleep contexts, better infant and parent sleep, and better child adjustment; (2) early coparenting around infant sleep will be a central mechanism by which both interventions exert their effects. This research is foundational to a broader understanding of coparenting processes that underlie successful family transitions and contributes to the refinement of a successful coparenting program. Study results will be of immediate use to obstetric and pediatric services interested in augmenting childbirth education material with information on coparenting practices in infant sleep contexts.