Relatively little research has focused on whether countries' political institutions affect their international trade relations. We address this issue by analyzing the relationship between regime type and trade policy. In a formal model of commercial policy, we establish that the ratification responsibility of the legislature in democratic states leads pairs of democracies to set trade barriers at a lower level than mixed country-pairs (composed of an autocracy and a democracy). We test this hypothesis by analyzing the effects of regime type on trade during the period from 1960 to 1990. The results of this analysis accord with our argument: Democratic pairs have had much more open trade relations than mixed pairs.