The object of the Legion of Mary is the glory of God through the holiness of its members developed by prayer and active co-operation, under ecclesiastical guidance, in Mary's and the Church's work of crushing the head of the serpent and advancing the reign of Christ.

The Legion of Mary is the largest apostolic organization of lay people in the Catholic Church, with about 3 million active members in almost every country of the world. The Legion of Mary has been active in the United States (USA) since 1931, has been approved by 7 Popes, and was endorsed by the Second Vatican Council. The main purpose of the Legion of Mary is to give glory to God through the sanctification of its members.

Members meet weekly for prayer, planning and discussion in a family setting. Then members do two hours of definite work each week in pairs and under the guidance of their spiritual director.