The case study shows that membership of the European Union and its predecessors has rarely commanded support among the UK’s two main political parties. The referendum on whether to remain in 1975 (only two years after entry, two previous applications for membership were rejected principally by France) was largely a devise by the Labour prime minister to avoid serious party division. The 2016 referendum, similarly was driven by Prime Minister Cameron’s attempts to manage division in the Conservative Party after some years of growth in anti-EU feeling among Conservatives and under pressure from UKIP drawing votes away from the Conservatives. Prior to the 2016 referendum attempts by the prime minister to renegotiate some of the UK’s membership terms with the EU were unsuccessful. The chapter outlines the referendum campaign, in particular the rival remain and leave campaigns and the main campaigning issues of immigration (sometimes conflated with ‘regaining sovereignty’) and economic wellbeing. The result is analysed in some detail, showing the significance of age and education as voting determinants but also giving a much more nuanced picture of how salient issues like immigration played out and the importance of other factors like location in explaining voter behaviour.