Against the background of the EU’s multifaceted crisis, i.e. financial and refugee crises, the growing security threat, Brexit, the deterioration of state of law in some member states, the growing gap between citizens and political elites, the political radicalization of an increasing number of citizens, etc. this book purports to reassess the social, legal, economic and moral dimensions of solidarity in the EU. The discussion on the challenges solidarity as the leading principle of EU integration currently faces focuses on fundamental questions vis-à-vis EU integration such as: are the EU’s integration and crisis management capacities already exhausted, has European integration reached its limits or will the EU be finally in the position to fully put into practice and further enhance solidarity, and hence, integration?