This chapter outlines the different analytical perspectives that can be used to study the EU. It first discusses three different integration theories (neo-functionalism, intergovernmentalism and postfunctionalism) and their spin-offs. These theories seek to explain why and how countries have decided to establish European cooperation and what role key actors (governments, interest groups, the public, politicians and civil servants) play in this. The chapter subsequently outlines theories of EU politics which seek to explain the actual functioning of the EU. In doing so it places a strong emphasis on the comparative politics approach, where the functioning of the EU is analysed by employing theories and concepts that are used in analysing domestic political systems. Additionally the chapter also discusses multi-level governance and federalism as two additional ways to understand EU politics. These theories provide complimentary insights in to the EU’s functioning. The choice to employ a certain theoretical perspective depends upon the types of questions asked and the actors that are of interest.