Questions surrounding the concept of legitimacy—the force that keeps a polity together, and whose absence causes it to shatter—are possibly the most important concern of a study of politics. M. F. N. Giglioli examines the shift to a distinctly modern understanding of the concept in Continental Europe, following the crisis of liberal rationalism in the late nineteenth century, and the search for new ways of envisaging the determinants of collective action into the twentieth century.The author examines certain aspects of the intellectual and political background of early twentieth-century theories of legitimacy elaborated by Max Weber and Antonio Gramsci. These theories are interpreted as the outcome of a contested process of redefinition of the concept, itself prompted by the social and political circumstances of the late nineteenth century, such as economic modernization and the attempt to incorporate the working class into the political system.This is the first book in a generation to offer a general reassessment of issues of legitimacy in political thought at the turn of the twentieth century. It examines the development of the concept in France, Italy, and Germany during the half-century or so following the Paris Commune. It discusses six key critics of classical Victorian liberalism on the revolutionary Left and the conservative Right. The political position and biography of each is a central focus of the study, as the culture of the age was decisively shaped by reflection on the social role of intellectuals.