"True Devotion to Mary" is universally acclaimed as the single greatest and most theologically authoritative book on the Blessed Virgin Mary ever to have been written. This work has had a tremendous impact on a number of the most significant and influential popes, from the late 19th Century right down to our own times: (1) Pope Leo XIII beatified de Montfort in 1888, adopted de Montfort's Mariological terminology (calling Mary the "Mediatrix" and "Co-Redemptrix"), and wrote no less than ten encyclicals on the Rosary; (2) Pope Saint Pius X, in 1904, wrote his key Marian encyclical, "Ad Diem...