This article seeks to go beyond two of the major limits of neo-institutionalist studies on institutional change: namely, the fact that they neglect both public policy reforms and the “transformative effects“ such reforms can bring about. It defines and operationalizes the concept of a “reform trajectory“, conceived of as a long-term succession of sequenced reforms, each having consequences for its successor and having a “transformative effect“ on the system of institutionalized public policies subject to reform as a whole. Based on our work on administrative and welfare state reforms, we outline seven principles to reconstruct the trajectory of public policy reforms by using process tracing.