To create a festschrift in honor of a scholar as important as Charles Tilly is a daunting task. To their credit, the editors and authors of Challenging Authority successfully provide a thoughtful and particularly readable glimpse into both the past and the future of the study of contentious politics, a field in which Tilly's contributions have been undeniably crucial. From more traditional interpretations of Tilly's work to innovations in chapters by Kim Voss and Marc W. Steinberg, this volume displays the wide array of applications and insights provided by the political process model for studying collective action, whether in medieval Spain or 1989 China. However, the volume moves only in fits and starts toward the new “relational structuralism” (xix) that the editors herald as coalescing around the study of collective action.