This study examined the individual and joint relationships of mature and immature defense mechanisms and the use of negotiation as a conflict resolution strategy with the co-parenting of divorcing couples. The responses of 71 divorcing couples to the study questionnaires were analyzed using the Actor–Partner Interdependence Model. Findings showed that both conscious use of negotiation and unconscious use of mature defense mechanisms for the purpose of conflict resolution were associated with the co-parenting of those parents who possessed these qualities, and that where one parent used mature defense mechanisms, the other participated more in his or her children’s lives and showed more cooperation. Almost all actor effects were forms of increased participation in the children’s lives. The lack of partner effects in the case of immature defense mechanisms and positive use of negotiation was discussed, and clinical implications were presented.