The goal of strengthening solidarity between European States is part of the DNA of the European Communities, which later became the European Union. The ECJ considers the willingness and reliability of the Member States to respect the common rules and principles irrespective of then prevailing national interests to be the starting point and core of solidary behaviour. In the primary law of the European Union, the principle of solidarity is recognised as a common value and is further concretised as a legal obligation in specific policy areas. A distinction can be made between solidarity between Member States, solidarity towards third countries and solidarity with EU citizens (social solidarity). Crises such as the financial crisis, the refugee crisis and the COVID-19 pandemic have put solidarity between Member States to the test. The behaviour of Member States revealed in the crises has shown an ambiguous picture. Solidarity-based political action ultimately depends on the willingness of Union citizens not only to pursue own interests through integration, but also to be ready to provide mutual support. Greater transparency about the advantages that the European Union and mutual support bring to all as a result could help to strengthen the sense of solidarity.
