Longitudinal and concurrent relations among positive and negative marital behaviors in 2 contexts and preschoolers' security of attachment were examined for 53 families. At 6 months postpartum, couples were observed in their homes during couple discussion and family play. At 3 years, parents completed the Attachment Q-Set (E. Waters, 1987); marital and parenting behavior was also observed. Interparental hostility during family play at 6 months predicted less secure preschooler-mother attachment. Greater marital conflict at 3 years was associated with less security with mother and father, whereas positive marital engagement at 3 years was associated with more secure child-father attachment. Mothers' parenting partially explained the linkages between marital behavior and child-mother attachment. These results highlight the impact of positive and negative marital behaviors on children's abilities to use their parents as a secure base.