This book considers why the level of party presidentialization varies from one country to another, and how constitutional structures and party genetics affect both the level and the degree it is present. Presenting an international collection of case studies from the US, Latin America, Australia, Japan and Europe, including France, Italy, Germany, Poland and the Ukraine, it examines how the presence of presidential features in political parties varies in terms of the constitutional framework. Highlights the importance of institutions in political life, the case studies provide empirical evidence that no stable presidentialization is possible outside regimes where a presidential dynamic is introduced by the institutions.