The 23 June 2016 referendum on the United Kingdom’s (UK) membership of, or exit from (Brexit), the European Union (EU) was seen widely as one of the most significant and potentially far-reaching events in UK and European politics and society. There had been a precedent in 1975 when, after only two-and-a-half years of membership, the UK voted by 67.2 per cent to 32.8 per cent to stay within the then European Economic Community (EEC), commonly referred to as the Common Market. In Northern Ireland (NI), the voting in 1975 resulted in a 52.1 per cent vote to stay in against 47.9 per cent to leave. The 2016 referendum took place largely, albeit not only, in response to the challenging rise of the United Kingdom Independence Party (UKIP), the demand within the euroskeptic wing of the Conservative PArty to put the issue of the UK’s EU membership to the electorate and the wish to satisfy disaffected elements of popular opinion. In 2013, the Conservative Prime Minister, David Cameron, had promised to legislate for an in/out EU referendum if the Conservative Party won the general election, and the party’s 2015 election manifesto declared that: ‘Only the Conservative Party will deliver real change and real choice on Europe, with an in-out referendum by the end of 2017’ (Conservative Party, 2015: 72). This article will assess the 2016 referendum in Northern Ireland, focusing on the following aspects: political parties, campaigning, interest groups, the result, and the aftermath.