In recent decades Europe?s political landscape has been marked by a notable rise in the use of mechanisms of direct democracy such as the referendum and the citizens? initiative. Our focus in this article is on the national referendums that are directly connected to the European Union (EU) integration process. These types of referendums are increasingly recognised by the scholarly community as the source of institutional instability across the wider EU polity. To explain the nature of this empirical puzzle is this article?s main objective. However, instead of pursuing intra-EU comparisons, as does much of the literature, we adopt a comparative perspective on the EU that involves the explicit comparison with other polities. In doing so, we bring to the fore a neglected dimension in the study of EU referendum politics: the operation of federal political institutions. We contend that cross-polity comparison of EU forms of direct democracy with other polities reveal insights that suggest a number of institutional models to overcome the sources of the present instability.