<Online Only>This chapter examines how institutional change in post-war Europe reconstituted inter-state, state society, and social relations in such a way as to restrain sovereignty, depoliticize the economy, and deradicalize politics. The constitutionalism that developed in the post-war era, and the transformation in state-society relations that it signalled, had international, European, and domestic dimensions, which were themselves intertwined. Constitutionalism contributed significantly to the process of de-democratization, in combination with a demobilization of the masses and a de-radicalization of parties of the Left. The transformation of political problems into technical or legal issues, along with the decline of parliamentarism as a touchstone of political legitimacy, and the constitutionalization of the European Treaties, would be facilitated by the relatively high levels of economic growth during the Trente Glorieuses, which permitted welfare corporatism to complement the constitution of a passive authoritarian liberalism. The chapter concludes by noting how this set in motion a dynamic that takes a sharper turn in the ‘new neoliberalism’ of the 1980s.</Online Only>