The dwindling popularity of globalization and international cooperation poses the issue of exiting an international union. An individually made exit decision is inefficient, as it neglects the losses of the other members. Fiscal transfers inside the union eliminate socially inefficient exits and restore the first-best outcome. When fiscal transfers are impossible, the union benefits from introducing exit costs during the formation process. Those costs are Pareto-optimal despite being a deadweight loss. If the union cannot fully commit to imposing exit costs ex post, it can use the anticipation of further exit decisions to increase its credibility. The paper also explores the scope for post-exit cooperation between the exiting country and the union. I show that both parties prefer a soft exit over a no-deal exit. However, the union might be reluctant to agree to a deal if it forms a precedent for the other union members. The model sheds light on Brexit and the UK-EU negotiations but also applies to other international unions.

全球化和国际合作的日益衰落提出了退出国际联盟的问题。单独做出的退出决定效率低下，因为它忽略了其他成员的损失。联盟内部的财政转移消除了社会效率低下的退出并恢复了最佳结果。当财政转移不可能时，工会可以从组建过程中引入退出成本中获益。尽管是无谓损失，但这些成本是帕累托最优的。如果工会不能完全承诺事后征收退出成本，它可以利用对进一步退出决定的预期来提高其可信度。本文还探讨了退出国与欧盟之间退出后合作的范围。我表明双方都更喜欢软退出而不是无协议退出。然而，如果一项协议成为其他工会成员的先例，工会可能不愿意同意该协议。该模型揭示了英国脱欧和英国与欧盟的谈判，但也适用于其他国际联盟。