Prior research has noted that although cooperative coparenting between resident and nonresident parents is beneficial to children, this form of shared parenting is relatively uncommon. Relying on nationally representative data from two waves of the National Survey of Families and Households (N = 628), this study examines the importance of nonresident fathers' and resident mothers' new marriages and new children for levels of cooperative coparenting and test whether changes in coparenting are linked to changes in parents' marital or fertility statuses. Consistent with prior studies, the data suggest that cooperative coparenting does not occur in most nonresident father families. Results suggest that changes to the nonresident father's family structure are of primary importance for cooperative coparenting, but that mother's family structure is relatively unimportant. (Contains 8 notes, 2 figures, and 2 tables.)