The economic and financial crisis affecting the European Union since 2008 has put solidarity on top of public and policy agendas. While solidarity between member states is an extensively discussed issue,, we know little about social solidarity between citizens and civil society organizations across borders. This paper assembles available evidence and strives to develop a conceptual and theoretical framework for the empirical analysis of transnational solidarity within the EU. It argues that it is not possible to apply standard wisdom on solidarity to the European level, given the societal and institutional complexity of the European Union. The paper proposes a conceptual, analytical and explanatory frame of reference that combines social and political dimensions of solidarity. Moreover, it stresses the need to differentiate between various levels of solidaristic relations, responsibilities and obligations within the EU, namely the micro-level (individual solidarity and its determinants), the meso-level (organizational fields and dynamics), and the macro-level (the social-structures of European societies¸ and the public debates on European solidarity).
