Set against the background of mid-twentieth-century institutional changes analyzed by Jürgen Habermas, we provide an account of new social conditions that compose “the public sphere” in the contemporary United States. First, we review recent developments in theorizing the public sphere, arguing they benefit from renewed attention to institutional changes in how that sphere operates. Second, we identify and summarize three lines of recent sociological research that document a new structural transformation of the contemporary public sphere: (1) civic communication through new media; (2) the professionalization of social movements; and (3) new, hybrid institutions such as think tanks, nonprofit foundations, and other public-private partnerships. Third, we argue that these new formations define a uniquely autonomous, interstitial social field. We conclude by discussing the implications of this synthesis for sociological theories of public life, arguing it can inform more effective study of the social infrastructure of democratic practice.