Phelan, William. (2012) What Is Sui Generis About the European Union? Costly International Cooperation in a Self-Contained Regime. International Studies Review, doi: 10.1111/j.1468-2486.2012.01136.x    It is widely agreed that the EU is a sui generis international organization, but current scholarship rarely specifies why. This paper identifies the EU as a “self-contained regime”, a treaty institution that imposes costly requirements on its member states but rejects the use of inter-state countermeasure and reciprocity mechanisms. As a self-contained regime, the EU is a puzzle because international relations theory emphasizes the importance of inter-state countermeasures as incentives for states to fulfill costly obligations, as is illustrated by scholarly debates on the politics of both trade and human rights regimes.