This article carries out an in-depth analysis of the complex meaning of solidarity within the EU legal framework. Solidarity is a multi-layered concept that serving as the basis for different policy-making choices of highly variable material substance, contributing significantly to the judgments of the CJEU. The point of departure in the analysis are references made to the notion of solidarity in the Founding Treaties. An important layer of its meaning derives from solidarity considered as a ‘value’. Important references are made to solidarity as a ‘principle’ or ‘spirit’ and there are additional layers of its meaning in the Treaties. In secondary legislation and the institutions’ communications, solidarity serves mainly as a basis for socially orientated policymaking. Following the analysis of the meaning of solidarity, I consider the notion of ‘solidarity acquis’ elaborated by Malcolm Ross that suggests that solidarity is one of the most effective tools in maintaining the consistency of the EU legal framework. Finally, the paper focuses on the case-law of the CJEU to conceptualize core legal implications of solidarity in order to establish whether solidarity may be recognized as a general principle of EU law.