Single-issue referendums -which give voters a say on specific European Union (EU) policies or general questions of European integration -were rarely employed before the 2000s, but they have since become commonplace. Examples include Greece's 2015 referendum on negotiations with the EU and International Monetary Fund (IMF), Hungary's 2016 referendum on the relocation of refugees between EU member states and the UK's 2016 vote to leave the EU. This article asks why we are seeing more single-issue referendums in the EU. Surveying different theoretical perspectives on the conditions under which such votes occur, it considers single-issue referendums as being driven by (1) the search for strategic advantage in a twolevel game, (2) domestic effects and (3) problems of consentification. Case studies of eight single-issue referendums show that domestic effects matter but offer limited evidence of hand tying. Most single-issue referendums, it finds, were called by governments wrestling with issues that could win legal approval but not political legitimacy. This instrument of direct democracy will remain a feature of EU politics, we contend, as member states wrestle with domestic effects and the challenge of (de)legitimating EU decisions through traditional means.