Rational choice and sociological institutionalism both understand the effect of Europeanization on the member states as a process of institutional change. The conceptions of the domestic impact of Europe as a resource-dependent process and a process of institutional adaptation, respectively, generate different propositions on the conditions, the process, the degree, and the outcome of domestic change. But neither resource dependency nor institutional adaptation provide a sufficient explanation for variation at the domestic level. Why do domestic actors respond differently to the opportunities and constraints provided by Europeanization, be they material or ideational? Why do some member-state institutions undergo more profound institutional change than others do, even if they face similar degrees of institutional misfit?

In order to address these questions, I combine assumptions (1) of rational choice and socio-logical institutionalism, (2) of resource dependency and institutional adaptation, and (3) of agency and structure within a historical institutionalist framework. This framework emphasizes the role of institutions in mediating the domestic impact of Europe (institution dependency).

Institution dependency denotes, first, that institutional adaptation to environmental changes is influenced by the strategies that actors choose in response and, second, that the choice of adaptational strategies depends on the institutions in which actors are embedded. This definition of institution dependency entails an understanding of actors' behavior and its relationship to institutions which is informed by historical institutionalism (Steinmo et al. 1992; Hall and Taylor 1996).