How and under what conditions does legitimacy affect processes of international institutional change? This article specifies and evaluates three causal mechanisms by which variation in legitimacy induces institutional change in international organizations (IOs) and argues that an important, yet hitherto neglected, source of legitimacy-based change is cognitive in nature. Using survival analysis, we evaluate these mechanisms with a novel dataset on the establishment of parliamentary institutions in thirty-six regional organizations between 1950 and 2010. We find that the empowerment of supranational secretariats, engagement with the European Union, and parliamentarization in an organization's neighborhood increase the likelihood of regional parliamentarization. This suggests that legitimacy judgments that draw on cognitive referents provide an important source of international institutional change. We illustrate the underlying cognitive emulation mechanism with a case study of parliamentarization in the Association of Southeast Asian Nations.
