A sample (N = 112) composed primarily of European American and middle-class two-parent families with a resident father and a 4-year-old child (48% girls) participated in a longitudinal study of associations between coparenting and father involvement. At the initial assessment and 1 year later, fathers reported on their involvement in play and caregiving activities with the focal child, and coparenting behavior was observed during triadic family interactions. Structural equation modeling was used to test cross-lagged associations between coparenting behavior and father involvement. Overall, paths from father involvement to coparenting behavior were significant, but paths from coparenting behavior to father involvement were not. Specifically, greater father involvement in play was associated with an increase in supportive and a decrease in undermining coparenting behavior over time. In contrast, greater father involvement in caregiving was associated with a decrease in supportive and an increase in undermining coparenting behavior. Multigroup analysis further showed that these cross-lagged relations did not differ for dual-earner families and single-earner (father) families, but these relations appeared to differ for families with focal daughters and families with focal sons. These findings highlight the potential for fathering to affect coparenting and the importance of the role of contextual factors in coparenting-fathering relations.