To a large extent, this process of transnationalization has been induced by European constitutionalization, which not only results in new opportunities for transnational actors to influence policy-making at the European level. It also expands the scope for cross-border exchanges, transnational socialization and policy transfer below the EU level. Transnationalization does not only result from further supranational integration, however. It also has roots in the longer term historical, socio-economic and cultural similarities of European states and societies and transnational links. The process is further supported by transnationally constituted social institutions like the Catholic Church. In an age of globalization, it is also strengthened by comparable economic challenges and similar needs for societal reforms. In view of these challenges, national societies need to be fully integrated in transnational networks and socialization processes if they do not want to be left behind.