This essay explores the question of how formal institutions change. Despite the importance assigned by many scholars to the role of institutions in structuring political life, the issue of how these institutions are themselves shaped and reconfigured over time has not received the attention it is due. In the 1970s and 1980s, a good deal of comparative institutionalist work centered on comparative statics and was concerned with demonstrating the ways in which different institutional arrangements drove divergent political and policy outcomes (e.g., Katzenstein 1978). In addition, scholarship in the comparative historical tradition has yielded important insights into the genesis of divergent (usually national) trajectories. Works in this vein include some classics such as Gerschenkron (1962), Moore (1966), and Shefter (1977), but also significant recent contributions such as Collier and Collier (1991), Skocpol (1992), Spruyt (1994), Ertman (1997), Gould (1999), and Huber and Stephens (2001). Finally, we have a number of analyses that address the issue of “feedback mechanisms” that are responsible for the reproduction of various institutional and policy trajectories over time (e.g., Pierson 1993; Skocpol 1992; Weir 1992b). Ongoing theoretical work centering on the concept of path dependence by Mahoney, Pierson, and others has lent greater precision to previous formulations based on the dual notions of “critical junctures” and “historical trajectories” (Mahoney 2000; Pierson 2000a). As these authors have shown, some of the major works in comparative historical analysis can be read as illustrations of path dependence in social and political development.