What is the “Miraculous Medal” and why is it called that?

The medal of the Immaculate Conception that has come to be called simply the “Miraculous Medal” dates back to an apparition of Mary to Saint Catherine Laboure, who was then a novice sister with the Daughters of Charity. On November 27, 1830, Our Lady appeared to her standing on a globe, with shafts of light streaming from her hands and the words, “O Mary, conceived without sin, pray for us who have recourse to thee,” surrounding the image. In the same vision, Catherine saw a capital “M” with a cross above it and below two hearts. Catherine seemed to hear a voice telling her to have what she saw struck as a medal and a promise that those who wore the medal would have the protection and intercession of the Mother of God. The first 1,500 of medals were distributed in 1832. Many miraculous favors were attributed to the use of the medal.