This book collects papers and materials provided for a Seminar Series hosted by the University of Catania Law Department on the multiple dimensions of solidarity models in international and European legal orders. The contributions refer, from different angles, to a multidisciplinary research Project on the EU’s potentialities as a socio-legal system increasingly challenged by solidarity patterns in a context of regional permacrisis. The Collection maps some of the project’s research lines exploring the sustainability of an authentic European solidarity policy guiding both the interactions between Member States and the social action of the States in their own internal legal orders.