The Legion of Mary is an international association of the faithful of the Catholic Church. Members are voluunteers who serve the Church.

It was founded in Dublin, Ireland, in 1921, as a Roman Catholic Marian Movement by Frank Duff, evolving into the largest apostolic organization of lay people in the Catholic Church. Today there are over 10 million members worldwide.

In order to join the Legion of Mary, one must be a practicing Catholic.

Active members serve God under the banner of Mary by practicing the Spiritual Works of Mercy.

The works of the Legion are directed towards everybody, without any discrimination. The members of the Legion are primarily engaged in the performance of the Spiritual Works of Mercy rather than works of material aid.