The book integrates philosophical, historical, and empirical analyses in order to highlight the profound roots of the limited legitimation of parties in contemporary society. Political parties’ long attempts to gain legitimacy are analysed from a philosophical–historical perspective pinpointing crucial passages in their theoretical and empirical acceptance. The book illustrates the process through which parties first emerged and then achieved full legitimacy in the early twentieth century. It shows how, paradoxically, their role became absolute in the totalitarian regimes of the interwar period when the party became hyper-powerful. In the post-war period, parties shifted from a golden age of positive reception and organizational development towards a more difficult relationship with society as it moved into post-industrialism. Parties were unable to master societal change and favoured the state to recover resources they were no longer able to extract from their constituencies. Parties have become richer and more powerful, but they have ‘paid’ for their pervasive presence in society and the state with a declining legitimacy. The party today is caught in a dramatic contradiction. It has become a sort of Leviathan with clay feet: very powerful thanks to the resources it gets from the state and to its control of societal and state spheres due to an extension of clientelistic and patronage practices; but very weak in terms of legitimacy and confidence in the eyes of the mass public. However, it is argued that there is still no alternative to the party, and some hypotheses to enhance party democracy are advanced.