This article first gives an overview of the countries and regions that are rich and poor, and how this pattern evolved over time. The following section analyses the extent to which socio-economic disparities are politically relevant in the EU, and highlights reasons why the rich–poor distinction is less relevant than standard political economy arguments would lead one to expect. The final section takes up a question that may become of unfortunate relevance for the cohesiveness of the Union, namely whether poor member states such as Greece are necessarily more crisis-prone, making the poor–rich distinction more salient in the future.