Referendums present a rare occasion for movements to have a central role in political developments and emerge from the shadow of the usually more dominant political parties. Tarrow and McAdam have argued that the interaction of parties and movements intensifies around elections: movements can mobilise proactively prior to elections, or reactively to their outcomes (McAdam and Tarrow, 2010: 534). The same can be said for party–movement interactions around referendums, with perhaps a greater emphasis on movements as key participants in campaigns themselves rather than simply reacting to political parties’ initiatives. Indeed, on multiple occasions, campaigns led by movements have defeated referendums introduced and backed by political parties, such as in the Canadian constitutional referendum in 1992 (Pammett and LeDuc, 2001) or the referendum on the first Lisbon Treaty in Ireland (Kissane, 2009).

Together with elections, referendums are perhaps the best-established form of mass democratic participation. Although there are many similarities between electoral and referendum campaigns, there are also some significant differences, particularly in terms of the latter's openness to broader participation. First, elections are by definition characterised by competition between political parties, while movements are limited to endorsing or opposing certain politicians or parties, and thus confined to the margins. Referendums, on the other hand, are more open to movement engagement. Certain states and regions even facilitate referendums triggered by popular initiatives (see Barankay et al, 2003). Second, elections are part of often well-established short-term electoral cycles centred on regular elections at the municipal, regional, national and European levels. Referendums are often the culmination of decades-long mobilisation, particularly those addressing questions of national sovereignty. Yet, the definitive result of these long mobilisations is often the result of a much shorter, more condensed referendum campaign (LeDuc, 2009: 139). Therefore, the timing of both the referendum campaign and the broader mobilisation that preceded the vote is a key element to understanding the dynamics of referendums. Third, all votes in referendums generally count equally, resulting in territorially extensive campaigns – in sharp contrast to the strategic concentration of resources on decisive marginal constituencies or party strongholds in elections. Finally, referendum campaigns are often more decisive in determining outcomes than are electoral campaigns because they are usually more volatile, often because of parties’ ambiguous roles (LeDuc, 2002b).