This chapter examines the role played by social movements in Jürgen Habermas’s social and political theory. Social movements appear as a theme at pivotal moments of certain of his key texts and serve as potential carriers of emancipatory social and political change. Yet their place in Habermas’s oeuvre has rarely been closely examined, at least not by scholars of Habermas. This may be partially due to the fact that the role he accords to social movements has always been tentative and ambivalent, and that his direct discussions of them are relatively minimal. However, social movements play a functionally vital role within Habermas’s political theory, which requires actors such as social movements to generate debate within the public sphere and open avenues within civil society for active citizenship in order to make the abstract ideal of deliberative democracy an empirical reality. As such, they and the role they play in Habermas’s writings deserve greater attention.