Differentiated integration (DI), whereby some MS opt out or are excluded from certain common EU policies for sovereignty or capacity reasons, may be thought to undermine the EU's functioning as what John Rawls called a fair scheme of cooperation, grounded in norms of impartiality and reciprocity. However, we argue that different forms of DI can be compatible with either fair cooperation between states on the model of Rawls' Law of Peoples or cooperation among citizens on the model of Rawls' two

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... principles of domestic justice. Meanwhile, the EU has features of both, being an international Union of states and a supraand trans-national Union of citizens. We defend the coherence of this combination and contend that DI can provide a justified mechanism for ensuring fairness between states remains compatible with fairness between citizens both within and across states. Indeed it offers a potential model for other forms of international cooperation.