On 23 June 2016, the United Kingdom voted by a 52 to 48 margin to leave the European Union. The result of the EU referendum was the latest and most dramatic expression of long-term social changes that have been silently reshaping public opinion, political behavior, and party competition in Britain and Western democracies. In this essay, we consider the underlying social and attitudinal shifts that made “Brexit” and the rise to prominence of the populist, right-wing U.K. Independence Party (UKIP) possible. Finally, we consider what these momentous developments reveal about the state of British politics and society.