From the Regnum Christi Website:
Regnum Christi is an apostolic movement at the service of mankind and the Church. It shares the charism of the priestly congregation, the Legionaries of Christ. Its current membership consists of about 30,000 youths, adults, deacons and priests in more than 30 countries.
In November 2004, the Holy See granted definitive approval to the Statutes of the Regnum Christi Apostolic Movement. The text of the decree explains that its mission is “to establish the Kingdom of Christ in the world through the sanctification of its members in the individual state of life to which each one is called by God, and through individual and organized apostolic action at the service of the Church and its pastors […]. Its specific charism is the same as that of the Legion of Christ: to know, live, and preach the commandment of love that Christ the Redeemer gave us through his Incarnation.” In this way, the Vicar of Christ confirmed the identity and charism of Regnum Christi.
Regnum Christi is precisely this: a movement for apostolate, a movement for evangelization. It is a movement in which each member has decided to take seriously and responsibly the great missionary commandment that Christ gave to all those who call ourselves his followers. The Legionaries of Christ and Regnum Christi members want to preach the Gospel fearlessly throughout the world, supported by the omnipotence of God and by the word of Christ who said: “I will be with you until the end of the world.”
Regnum Christi fosters a deep ecclesial and missionary spirit in its members. As a dynamic organization, it strengthens their spirit of initiative and reminds them of their baptismal responsibility to make the faith the engine of their daily life in their personal, family, parish, professional, and social circles.