The European Union (EU) is a grouping of states from Western, Eastern, and Central Europe. Those interested in politics view the EU with great interest because it is unique among regional and international power arrangements. Even non–political scientists study the entity; following its 2004 enlargement, it represented approximately 450 million people and 25 percent of the world's economic production, making it a significant international actor.

States created the EU and states make up its members. Unlike most other international organizations, however, the EU holds a measure of power over members' policies, especially in the realm of economics. This difference has led to debate about whether the EU has an intergovernmental (states alone hold power) or supranational (states and EU institutions together hold power) character. The answer depends on where one looks—which institutions and policy areas—as evidence for both characterizations exists. In the early twenty-first century students...