Structure and Change in Economic History is the theme of the 2026 meeting. Many economists and historians have presented powerful arguments for the importance of institutions in shaping economic outcomes. Distributional considerations are often considered as paramount drivers of institutional change or stasis. Thanks to a rising tide of data, we have made much progress in studying structure—namely, measuring the causal impact of a very wide variety of policies and institutions. We have made far less progress in understanding institutional diffusion or in understanding the persistence of institutions that inflect aggregate welfare or inequality. In both cases, these are fundamentally endogenous processes. Our challenge as a discipline is how to bring to bear the methods of causal inference to the process of institutional change over the long term. Meeting this challenge forces us to consider how institutional change is shaped by history, the efforts of individuals and organizations, and economic shocks, including new technologies. We call for research that unites the analysis of which policies or institutions work best, and the circumstances of their adoption.