This volume is dedicated to the principle of solidarity. It examines the role of solidarity as a legal principle and as a component of public policies in eight European countries — Denmark, France, Germany, Greece, Italy, Poland, Switzerland and the UK — and at the level of the European Union. It particularly focuses on developments in three areas: unemployment, immigration and asylum, and disability. The analyses show that solidarity is a common constitutional principle across the eight countries, and is thus a legitimate source of law, court rulings and policymaking. In the fields of unemployment, migration and disability, the legal frameworks are implicitly or explicitly committed to solidarity, but solidarity measures in these policy areas have been severely weakened since the various crises affecting the EU and other principles (such as security, competition and austerity) have prevailed. With contributions by Christian Lahusen, Veronica Federico, Deniz Neriman Duru, Thomas Spejlborg Sejersen, Hans-Jörg Trenz, Manlio Cinalli, Carlo de Nuzzo, Ulrike Zschache, Maria M. Mexi, Nicola Maggini, Janina Petelczyc, Eva Fernández G.G., Délia Girod, Tom Montgomery, Simone Baglioni, Ester di Napoli, Deborah Russo, and Tania Abbiate