I consider the influence of domestic political institutions on the ability of leaders to establish bilateral cooperation in the international system. Leaders operating in different domestic institutional environments have differing abilities to commit credibly to future courses of action, to accept the costs of policy failures, and to adjust to changes in the international environment. Using game theory, I deduce hypotheses about the effects of domestic institutional structures on the likelihood of cooperation. My model suggests that jointly democratic dyads and jointly autocratic dyads will cooperate more readily than dyads composed of one democracy and one autocracy. Analysis of COPDAB events data reveals evidence commensurate with these hypotheses. This research suggests that international cooperation theory will benefit from consideration of the influence of domestic politics on leaders' decisions, but that this influence can only be fully understood in the context of strategic behavior in the international system.