The EU is cloaked in expressions of solidarity. Despite the fundamental role that solidarity plays, cracks have appeared and become more evident across Member States. The euro – a transnational single currency – was a bold endeavour when first established, and its adoption was expected to generate a leap forward for by making European integration stronger, and more resilient. The prolonged battle of the sovereign debt crisis that emerged in 2009 tested the limits of solidarity: a confrontation waged on multiple levels, playing into constitutional frameworks and socio-economic divisions, and exacerbating fault-lines between states. Yet despite frequent arguments made to the contrary, solidarity was a feature of the financial crisis, albeit of a particular kind. The legitimate expectation of what role different concepts of solidarity ought to have played (particularly where fiscal redistribution is concerned), compared to the role it actually served, ensured that an expectations deficit opened. This chapter examines solidarity within the EU’s legal framework in the context of the Eurozone crisis. It analyses the ramifications of the idea of solidarity, variously defined, and the implications it may have for the future direction of the Union as it faces ever-greater challenges.