Jeffrey T. Checkel

International institutions are a ubiquitous feature of daily life in many world regions, and nowhere more so than contemporary Europe. While virtually all would agree that such institutions matter, there is less agreement on exactly how they have effects. This special issue brings together European Union specialists and international relations theorists who address the latter issue. In particular, we explore the socializing role of institutions in Europe, with our central concern being to better specify the mechanisms of socialization and the conditions under which they are expected to lead to the internalization of new roles or interests. Drawing on a multifaceted understanding of human rationality, we consider three generic social mechanisms—strategic calculation, role playing, and normative suasion—and their ability to promote socialization outcomes within international institutions. This disaggregation exercise not only helps consolidate nascent socialization research programs in international relations theory and EU studies; it also highlights points of contact and potential synergies between rationalism and social constructivism.For comments on earlier versions, I am grateful to two anonymous referees, IO editors Lisa Martin and Thomas Risse, as well as to John Duffield, Alexandra Gheciu, Liesbet Hooghe, Peter Katzenstein, Ron Mitchell, Frank Schimmelfennig, Martha Snodgrass, and Michael Zürn. More generally, thanks are owed to all the project participants for numerous and valuable discussions on the themes addressed in this volume.

Building on the empirical findings of the preceding articles, we advance three arguments. First, while socialization research has typically been construed as constructivism's home turf, this volume's emphasis on mechanisms and scope conditions reveals that rational choice has much to contribute here as well. We develop this claim by undertaking a “double interpretation” of each essay, which allows us to advance more fine-grained arguments connecting the two social theories. Second, while there are good conceptual reasons for expecting a predominance of international socialization in Europe, the empirical cases instead suggest that its effects are often weak and secondary to dynamics at the national level. We make sense of this puzzle by reasoning more explicitly in longitudinal terms, by drawing on work on European identity, and by noting that students of European socialization—as well as integration—have much to gain by “bringing the domestic back in.” Finally, while our collaborators have demonstrated the empirical and theoretical benefits of combining a social ontology with a positivist epistemology, this comes at a cost, with normative perspectives neglected. This matters—and all the more so in a Europe marked by supranational constitution- and polity building. Socialization dynamics may well take us beyond the nation-state, but their legitimacy and governance implications bring us back—forcefully—to it.We are grateful to the project participants and contributors to this volume for valuable discussions on the themes addressed here. For detailed comments on earlier versions of this essay, we thank two anonymous reviewers, the IO editors, Peter Katzenstein, and Ron Mitchell.