This chapter highlights sovereignty as another concept that, like governance, has shaped Brexit, and is influencing the new EU-UK relations. It argues that the entire process of leaving the EU can be explained in light of the peculiar British conception of sovereignty. It also clarifies how this legal and political view seems at odds with the reality of global governance and transnational regulation and cannot be reconciled with European integration. The chapter explores how and why the idea of sovereignty proved so powerful in the Brexit process and confirms what a ‘sovereignty-first’ Brexit entailed. It addresses why the UK opted for this form of future relationship with the EU in the Trade and Cooperation Agreement (TCA).