Secret of Mary is a book by Saint Louis de Montfort

Louis de Montfort

St. Louis-Marie Grignion de Montfort was canonized in 1947. He was a French priest and known in his time as a preacher and author, whose books, still widely read, have influenced a number of popes....

 on the Roman Catholic theme of devotion to the Blessed Virgin Mary.

The book is published by Tan Books but is also available free online. It complements de Montfort's other books the Secret of the Rosary

Secret of the Rosary

The Secret of the Rosary is a book about the Holy Rosary written by Saint Louis de Montfort a French priest and Catholic saint who died in 1716. The English translation of the book bears the Imprimatur of Archbishop Thomas E...

 and True Devotion to Mary

True Devotion to Mary

True Devotion to Mary is a book by Saint Louis de Montfort on the Roman Catholic theme of devotion to the Blessed Virgin Mary.The book is published by Montfort Publications , Baronius Press, TAN Publishing and Aventine Press but is also available online...

.

Saint Louis de Montfort's books attracted attention in the 20th century when in an address to the Montfortian Fathers, Pope John Paul II

Pope John Paul II

Blessed Pope John Paul II , born Karol Józef Wojtyła , reigned as Pope of the Catholic Church and Sovereign of Vatican City from 16 October 1978 until his death on 2 April 2005, at of age. His was the second-longest documented pontificate, which lasted ; only Pope Pius IX ...

said that reading one of de Montfort's books had been a "decisive turning point" in his life.