At the apex of foreign policy making in all governments or ruling parties are actors with the ability to commit the resources of the government and the power to prevent other entities within the government from reversing their position—the ultimate decision unit. Although this decision unit may change with the nature of the policy problem and with time, its structure will shape a government's foreign policy. In this paper we propose three types of decision units: predominant leaders, single groups, and multiple autonomous actors. Each of these exists in one of several conditions that help to determine whether the decision unit affects foreign policy largely through the pre-existing knowledge, beliefs, and style of those participating in the unit (a self-contained unit) or whether factors outside the decision unit must be taken into consideration in understanding the results of the decision-making process (an externally influenceable unit). The hypotheses that self-contained units will engage in more extreme foreign policy behavior than externally influenceable units and that single group decision units will show more extreme foreign policy behavior than those comprised of multiple autonomous actors are examined using data from twenty-five nations during the decade from 1959 to 1968.