As work and organizational reality become increasingly "post-bureaucratic," the conventional and stable bases of a person's authority-their position, their expertise, or the acquiescence of a subordinate-are eroding. This evolution calls us to revise our understanding of authority, and to consider more deeply how it is achieved in contexts that are both fluid and fragmented. Building on a six-month autoethnography of a consulting assignment, we show that authority is a practical, relational, and situated performance. It exists in a tension between two mirroring processes, activation and passivation, through which relations are either leveraged or downplayed to shape the situation and steer collective action. Our study also reveals that the performance of authority involves not just people, but also a broader range of actants, including artifacts and abstract entities. In line with current research on performativity in organizations, our findings contribute to the relational program on authority and the revelation of its sociomaterial dimension. Thus, we provide an action-based understanding of authority that is better suited for the study of post-bureaucratic organizing.