The Legion of Mary was founded in Dublin, Ireland on 7 September 1921. It is a lay Catholic organisation whose members are giving service to the Church on a voluntary basis in almost every country.

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 in Mary’s and the Church’s work.

The unit of the Legion of Mary is called a praesidium, which holds a weekly meeting, where prayer is intermingled with reports and discussion. Persons who wish to join the Legion must apply for membership in a Praesidium.