This study addresses two limitations of coparenting research: first, little research on coparenting has been conducted with families of adolescents, and second, there is little understanding regarding the child and family contexts in which coparenting is most salient. The longitudinal relation of coparenting conflict to parenting and adolescent maladjustment across 3 years was investigated among 516 2-parent, 2-adolescent families. Coparenting conflict predicted as much or more unique variance in parenting and adolescent adjustment as did marital quality and disagreement together. After controlling for stability, coparenting conflict predicted mothers' and fathers' negativity and adolescent antisocial behavior (but not depression). Importantly, the influence of coparenting conflict in all cases varied as a function of family type, adolescent gender, or initial level of antisocial behavior, or all. The implications of these results for family processes in different relational and developmental contexts are discussed.