This article integrates institutional and rational choice approaches to policy making to explain the emergence of delegative democracy in presidential systems. Delegative democracy, in essence, is a polyarchy which violates the rules and norms that secure the checks on the effective political power of democratically elected presidents at the horizontal level of the relations of the executive, legislature and judiciary. The article argues that delegative democracy is the result of the interaction of two variables: the strength and types of presidents' legislative powers and the configuration of institutional and partisan veto players. Strong, proactive legislative powers and weak veto players permit presidents to establish a delegative democracy; weak, reactive legislative powers and strong veto players hamper the emergence of delegative democracy. This general assumption explains why presidentialism in South Korea and in the Philippines developed in different directions in the 1980s and 1990s. The analysis shows that in case of moderate legislative powers of the president, the number, coherence and ideological distance of partisan veto players becomes particularly important. It suggests that studies of democratic regimes should give special emphasis to the rules regulating the distribution of legislative powers between presidents and parliaments and the configuration of veto players.