This study investigated relations between father involvement in caregiving and play and coparenting behavior using self-report and observational data from 80 two-parent families of preschool-aged children and examined parents' nontraditional beliefs about fathers' roles and family earner status as moderators of these relations. Results indicated that greater father involvement in caregiving and play was associated with less observed undermining coparenting behavior in dual-earner families. Conversely, greater father involvement in caregiving was associated with less perceived supportive and greater perceived undermining coparenting behavior in single-earner families. Father involvement in play was not related to coparenting behavior among single-earner families. This study highlights the importance of considering parental employment patterns and the multidimensional nature of fathering behavior when studying fathering and coparenting.