This edition provides the correspondence (in French) between Victor De Buck and two Russian converts to Roman Catholicism, Ivan Sergeevich Gagarin and Ivan Matveevich Martynov (who came to be known respectively as Jean-Xavier Gagarin and Jean Martynov). De Buck was a Belgian Jesuit, a Bollandist for the last twenty-six years of his life, working on volumes vii–xiii of the October volumes of Acta Sanctorum; he was an enthusiast for ecumenism (somewhat naïve, according to his contemporaries) and, among many other things, composed conciliatory essays on the procession of the Holy Spirit and the question of the afterlife. He was interested in the Oxford Movement, and especially Pusey, but his main ecumenical concern was union with the Orthodox. His correspondents were two Russians, one from Moscow, the other from Kazan, both of whom converted to Roman Catholicism and joined the Society of Jesus, both, within a couple of years of each other, passing through the same Jesuit training – noviciate at Saint-Acheul and scholasticate at Laval, both spending some time in Belgium. Both had diverse and interesting careers as Jesuits; both were associated with the Œuvre des Saints-Cyrille-et-Méthode in Paris. Gagarin spent part of his life in the Lebanon; Martynov was more consistently associated with Paris, and participated in Vatican I. Gagarin was an aristocrat, with a diplomatic career behind him; Martynov was of more humble origin, and joined the Jesuits straight after his brilliant degree in philosophy at St Petersburg. The correspondence is vast (more than 1,200 pages on DVD).