▪ Abstract  The growing use of institutional analysis in the study of the European Union (EU) has improved EU scholarship and rendered it more integral to the discipline of political science. Institutionalist analyses differ regarding the theoretical role of institutions and actor preferences. We classify institutionalist approaches to the EU by their theoretical treatment (exogenous or endogenous) of institutions and preferences. Analyses at the research frontier transcend these categories and offer the promise of an improved understanding of EU politics and a greater contribution by EU studies to the broader discipline of political science.