ABSTRACT
This chapter introduces the concept of differentiated integration and provides an overview of integration theory, followed by a presentation of the main theories of European integration: intergovernmentalism, supranationalism, and constructivism. The chapter begins with a presentation of intergovernmentalism by explicating its theoretical roots in rationalist International Relations (IR) theory and then move on to concrete propositions on European integration. In contrast to intergovernmentalism, supranationalism has a transformative ontology, it holds the international system is not bound to be anarchical but can be transformed through processes of institutionalization. IR theories traditionally assume that states are the central actors in international politics and they act in a context of anarchy that is in the absence of a centralized authority making and enforcing political decisions. Supranationalists have traditionally subsumed mechanisms of transformative change under the label of spillover. In spillovers Ernst Haas, the central mechanism to explain the 'expansive logic' of European integration.
