The Fifth Cleavage: Genealogy of the Populist Ideology proposes an in-depth analysis of populism, as one of the central phenomena in the contemporary public and political debate. In particular, this study aims to investigate the causes of the emergence of populism and its possible effects on the political system and on the democratic institutions. The central thesis of the book is that populism is originated by a cleavage between two opposite groups - the people and the elite - which appeared for the first time soon after the democratic revolutions of the 17th and 18th centuries. This cleavage is not constantly active; but it tends to reactivate itself only under certain circumstances, when certain critical junctures occur, thus giving rise to different "waves" of populism. When the "populist cleavage" is active, the other lines of division and conflict (of class, of religion, etc.) lose their relevance. What are the features of this cleavage? What kind of relationship does it have with the well-known traditional cleavages (capital-labor, state-church, urban-rural, center-periphery)? What are the characteristics of the recent "wave" of populism? And what are its effects on the functioning of democracy? These are the main questions to which this book is devoted.