This thesis examines the role of religion in national-EU relations. The focus is on how EU membership (or potential membership) may affect nations of a particular religious background in a particular way and, furthermore, whether religious difference affects national-EU relations in a particular way. The study is based on an internal perspective to two countries-Greece and Turkey-whose religious traditions stand outside a 'core' of religious traditions within the European Union (that is, Roman Catholicism and Protestantism). On the basis of these two cases I argue that neither religion per se (as theology or doctrine), nor the prevalence of a particular faith are definitive factors in national-EU relations. Rather, it is mainly in the domain of institutional interests of the `church' vis-ä-vis the 'state', that we find religion influencing national-EU relations. These institutional interests are, in turn, shaped by the relationship between religion and national identity in each case, and the relationship between 'church' and 'state'. The differences in these relationships in the cases of Greece and Turkey yield vast differences in the way 'religion' affects national-EU relations. This thesis examines the role of religion in national-EU relations. The focus is on how EU membership (or potential membership) may affect nations of a particular religious background in a particular way and, furthermore, whether religious difference affects national-EU relations in a particular way. The study is based on an internal perspective to two countries-Greece and Turkey-whose religious traditions stand outside a 'core' of religious traditions within the European Union (that is, Roman Catholicism and Protestantism). On the basis of these two cases I argue that neither religion per se (as theology or doctrine), nor the prevalence of a particular faith are definitive factors in national-EU relations. Rather, it is mainly in the domain of institutional interests of the 'church' vis-ä-vis the 'state', that we find religion influencing national-EU relations. These institutional interests are, in turn, shaped by the relationship between religion and national identity in each case, and the relationship between 'church' and 'state'. The differences in these relationships in the cases of Greece and Turkey yield vast differences in the way 'religion' affects national-EU relations. As background information to the interview research, secondary sources are used to explain the relationship between religion and national identity, and between 'church' and 'state' in each case.