Solidarity has become a strongly debated issue within the European Union. Ongoing conflicts between member states about financial solidarity with states affected severely by the economic crisis of 2008 and about fair burden-sharing with regard to the high numbers of refugees show the difficulties of living up to the standard of solidarity which the EU lists in its treaties as one of its guiding principles. At the same time, the debate unveils that solidarity is highly contested. The reservations of EU member states to share the burdens regarding the costs of the economic crisis and the migration inflow can be criticised as a lack of interstate solidarity and a prioritisation of national interests; they also evidence a more fundamental difficulty in agreeing on adequate public policies and coordinated problem-solving strategies. Governments are sensitive to nationalist and populist mobilisations and parties, whose electoral successes seem to limit the readiness of member states to engage beyond what might be conceived of as an instrumental and utilitarian solidarity of 'quid pro quo'. More than that, nationalist and populist parties contest the idea of European solidarity precisely in the name of national solidarity, and the need to defend national communities against outside interventions. Hence, controversies about solidarity prevail within the public sphere. These debates, however, have paid more attention to interstate solidarity, thus marginalising another topic that is much less discussed and researched: European social or civic solidarity. In fact, even though we might expect that both dimensions are interrelated, it is necessary to differentiate between solidarity among states and solidarity between European citizens, between the 'intergovernmental' and 'transnational' dimensions of solidarity, and between the 'vertical' support of interstate solidarity by citizens and the 'horizontal' engagement of citizens in cross-border relations of support and help (Apostoli, 2012: 4). Very little is known about the amount of transnational solidarity and the effects of