The books in this collection are designed to gather together the reflections and debates of those people who, through their research, are contributing to renewing knowledge about the relations between Christians and Jews in the Middle Ages, as a kind of mirror in which to analyse the paths of diversity, plurality and complementarity. This first volume contains the speeches and debates of a group of renowned French and Spanish medieval specialists who came together in Carcassonne for some days in October 2003 to analyse the sources for research into the relations between ones and the others and to debate the keys for interpreting the knowledge of a permanent way of dealing with each other, which has left a deep impression on European identity.