Since the EU treaties constitute solidarity as one of the EU’s fundamental values (Articles 2, 3 (2) TEU). In a community of law, the validity of this value depends on its capacity as a legal principle. This chapter asks what, if anything, the case law of the Court of Justice (ECJ) contributes to the discursive exegesis of solidarity as a principle of EU Constitutional Law. In order to answer this question, it offers an empirical analysis of the Court’s case law framing the notion of solidarity, providing a unique database evaluating all 122 cases elaborating on the concept. The analysis distinguishes three categorial types of solidarity (solidarity as charity, as mutual obligation and as risk mitigation) and three functional types of solidarity (embedding individual rights, embedding the Internal Market, rejecting limiting effects of national solidarity). The chapter identifies a number of missed opportunities, and a high degree of inconsistency. A more assertive and consistent approach to solidarity could, however, contribute to supporting a more inclusive constitutional discourse on European integration than the mere reliance on liberal constitutional principles.