This chapter examines the so-called ‘Brexit’ phenomenon, the first time an existing EU member state has voted in a referendum to leave the Union. The chapter examines the historical context that shaped the UK’s decision to join the EEC and its subsequent relationship with the EU. It charts the events leading to the EU referendum, including the campaign and explains the reasons for the narrow ‘Leave’ vote in the referendum. The Brexit negotiations under Article 50 are discussed by focusing on process, actors, and outcomes, specifically the content of the March 2018 Draft Withdrawal Agreement. The penultimate section of the chapter explains Brexit by drawing on the extant European integration literature with a focus on the concepts of disintegration, differentiated integration, Europeanization, and politicization, while surveying the likely scenarios for a future EU–UK relationship. The chapter ends discussing the impact and implications of Brexit for the EU.