Abstract We review arguments and empirical evidence in the comparative literature that bear on the differences in the survival rates of parliamentary and presidential democracies. Most of these arguments focus on the fact that presidential democracies are based on the separation of executive and legislative powers, whereas parliamentary democracies are based on the fusion of these powers. The implications of this basic distinction lead to radically different behavior and outcomes under each regime. We argue that this perspective is misguided and that one cannot deduce the functioning of the political system from the way governments are formed. Other provisions, constitutional and otherwise, also affect the way parliamentary and presidential democracies operate, and these provisions may counteract some of the tendencies that we would expect to observe if we derived the regime's performance from its basic constitutional principle.