This study examined parent characteristics as correlates of coparenting behavior in 57 primiparous couples. Parents' negative emotionality and perceptions of maternal acceptance in childhood, mothers' beliefs about fathers' roles, and observed marital behavior and family socioeconomic status were assessed during the third trimester of pregnancy, and coparenting behavior was observed at 3.5 months postpartum. Couples who exhibited high-quality marital interaction showed higher supportive coparenting behavior, but couples who showed lower quality marital interaction demonstrated higher supportive coparenting behavior when mothers held more progressive beliefs about fathers' roles. Couples showed more undermining coparenting behavior when family socioeconomic status was lower and when fathers were higher on negative emotionality. Greater perceived maternal acceptance in childhood was only associated with lower levels of undermining behavior when prenatal marital interaction was high in quality. Thus, the characteristics of both parents, especially in combination with preexisting marital behavior, are important determinants of coparenting behavior.