Father Arintero attained great renown in his native Spain for his profound learning and his personal sanctity. Because of his success as the champion of the true traditional doctrine in mystical theology, he is acclaimed the precursor of the current movement toward the realization of mystical ideals. To forestall any criticism of Father Arintero's style and method of procedure, let it be remembered that he looked upon the sublime truths of the supernatural life as one would gaze upon a precious stone, turning it this way and that to catch its full brilliance and luster. There may be some persons who will question the wisdom of including excerpts from the writings of modem mystics that as yet are unknown to most readers. Many of these souls were under the guidance of Father Arintero, and he saw in their experiences the perpetual vitality of the mystical power of the Church. He uses them, then, to show that the heights of the mystical life are by no means a relic of the past, but that there are souls even today who have scaled and are scaling the mount of perfection. I here express my deep gratitude to the Very Reverend Father Provincial of the Province of Spain, who gave permission for this English translation of La Evoluci6n Mistica; to the Very Reverend Father Peter O'Brien, O.P., Provincial of the Province of St. Albert the Great, for his kindly interest and unfailing encouragement; to Father Vitalis Fueyo, O.P., of Avila, Spain, for his careful reading, and checking of the entire translation; and to the Very Reverend Father Sabino Lozano, O.P., of Salamanca, Spain, for his helpful advice. Finally, acknowledgment and gratitude must be voiced to the following publishers and individuals for permission to quote from their works: Mr. Allison Peers, London, and Sheed and Ward, New York and London, for quotations from the Complete Works of Saint Teresa; Bcnziger Brothers, New York, and Burns Oates and Washbourne, London: the English version of the Summa theologica and the Summa contra Gentiles; Newman Bookshop, Westminster, Maryland: Lallemant's Spiritual Doctrine; Mr. Allison Peers, Burns Oates and Washbourne, Newman Bookshop: Complete Works of St.John of the Cross; Mr. Louis Bernicken, Mt. Vernon, Ohio: the Ven. Mary Agreda's The City of God; Rev. Father Anselm Townsend, O.P., Oak Park, Illinois, translator of Gardeil's The Gifts of the Holy Ghost in the Dominican Saints; Routledge and Kegan Paul, London: Poulain's The Graces of Interior Prayer; B. Herder Book Co., St. Louis, Missouri: Tixeront's History of Dogmas and Caussade's Abandonment to Divine Providence. The quotations from Froget's The Indwelling of the Holy Spirit are reprinted with permission of the copyright owners, the Missionary Society of St. Paul the Apostle in the State of New York. May this book serve as an impetus to those who are still timid about venturing into the realms of the supernatural life. May it clarify the problems and difficulties which beset those who are well along the way and those whose task it is to direct such souls.