In Paris, on June 6, 1830, the Lord appeared to the young (age 24) Daughter of Charity novice Catherine at Mass, and again on the nights of July 18-19 when she was summoned to the chapel by a beautiful "child clothed in white" to converse with the Virgin Mary. Catherine was told prophecies and charged with "a mission" that manifested itself on November 27 in an early morning (5:30am) appearance of the Blessed Virgin who was "clothed in white" standing on a globe and "a serpent."Hat Tip: Catholic Fire
Rays of light issued forth from rings on her fingers and Catherine was told to commission a medal of what she was seeing. Then, turning the letter "M surmounted by a bar and a cross" underneath which were the hearts of Jesus and Mary all surrounded by the words "O Mary, conceived without sin, pray for us who have recourse to thee."
Catherine heard the voice tell her, "Have a medal struck after this model. All who wear this medal will receive great favors. They should wear it around the neck . Favors will abound if worn with devotion." Catherine's mission was to ensure that the medal was made and to spread Mary's message of love and compassion.
Many healings, conversions and other miracles have been documented by those who have faithfully worn the 'Medal of the Immaculate Conception' as the Miraculous Medal was originally called.
There are numerous Miraculous Medal Associations throughout the world. They are united under the care of the Congregation of the Mission (Vincentians or Lazarists), the religious order founded by St. Vincent de Paul. Membership contributions go to spread devotion to the Virgin Mary and to support the work of the Vincentians. Each Association maintains a shrine and usually has some type of publication for members.