At the origin of the creation of the Amitié-Judéo-Chrétienne section of Lille, there is, among others, Sister Geneviève Gendron, a Salesian Sister who was committed to Ecumenism before the War. She was overwhelmed by the discovery of Jules Isaac’s book, Jésus et Israël, in early 1949. She wrote to Jules Isaac and exchanged letters until his death in 1963, telling him what she did in order to promote the Jewish-Christian dialogue. Starting from Lille, where she stayed until 1951, and later from Italy where her Congregation sent her, she asked for advice. 45 letters from Sister Gendron to Jules Isaac have been found in the archives kept in the Library Méjanes of Aix-en-Provence (unfortunately, only a few answers from Jules Isaac have been preserved ; they are displayed in this issue). These documents shed light on the beginning of the Amitié Judéo-Chrétienne de France and the evolution of the issues discussed within the Roman Catholic Church on the subject of the Jews. These letters, here published, are copiously annotated, and introduced by Olivier Rota who presents Sister Gendron’s trajectory and the importance of her effort.