This article explores important aspects of the relationship between political leadership and institutional power, comparing the different forms that presidential institutions have taken across the world, and identifying the relationship between these structures and social, political, and economic outcomes. Semi-presidential systems are distinguished from presidential systems, and within the former a distinction is made between president-parliamentary and premier-presidential regimes. Some scholars have argued that presidential regimes are less conducive than parliamentary ones to the successful transition from authoritarian rule to democracy, but the empirical evidence is contradictory. Recent research has, however, drawn attention to finer distinctions within the various broad categories of presidentialism, focusing on more precise institutional arrangements and trying to identify which are more, and which are less, consonant with the consolidation of democracy.