This paper is intended to contribute to the explanation and prediction of behavior in interunit decision making and the relative quality of decision outcomes under varying conditions. It focuses on the interaction processes which occur in joint decision making settings. It is first descriptive, but with prescriptive implications for how one structures the decision making situation. Two purposive decision processes, problem solving and bargaining, are instrumental to the formal purposes of the interunit relations. Two purposive social processes, identity reinforcement and identity conflict, are expressive of the way parties view themselves, compared with how they are viewed by each other.