The Legion of Mary is a lay apostolic association of Catholics who, with the sanction of the Church and under the powerful leadership of Mary Immaculate, Mediatrix of all Graces, serve the Church and their neighbour on a voluntary basis in about 170 countries.

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 Churches work.

The unit of the Legion of Mary is the praesidium, which holds weekly meetings, where prayer is accompanied by reports and discussion. The Legion sees as its priority the spiritual and social welfare of each individual.

Members participate in the life of their parishes through visitation of individuals, families, and the sick, both in their homes and in hospitals and many other aspects of work sponsored by their local parish. Every member is required to undertake a weekly apostolic work in the spirit of faith and in union with Mary. Seeing and serving Christ in the sick and marginalised is a vital part of the legionary apostolate.

The basic unit of the Legion is called a praesidium, which is normally based in a parish. To be an active legionary it is necessary to apply for membership in a praesidium, which holds a weekly meeting and allocates weekly apolostic tasks to its members, who generally work in pairs. After a successful period of probation, members 18 years or older are asked to are called to make the Legionary Promise, which is directed to the Holy Spirit. Realising the need for a strong support of prayer, the Legion also has auxilliary members, who associate themselves with the Legion by undertaking a service of prayer in its name, but do not attend weekly meetings or undertake acts of work.