SUMMARY: Twenty-five years after the conclusion of the II Vatican Council, the publication of the Decree on Missionary activity Ad Gentes, and fifteen years after the apostolic exhortation Evangelii Nuntiandi by Pope Paul VI, John Paul II promulgated the encyclical Redemptoris Missio. This document has as its goal an interior renewal of faith and Christian life. Missionary activity renews the Church, revitalizes faith and Christian identity, and offers fresh enthusiasm and new incentive.The present study treats the responsibility of the christian lay faithful in missionary action. «Since the entire Church is missionary by its nature and since the work of evangelization is to be viewed as a fundamental duty of the people of God, all the Christian faithful, conscious of their own responsibility in this area, are to assume their own role in missionary work» (Canon 781). As members of the Church, lay faithful have responsibility to partecipate in missionary action. The Encyclical Redemptoris Missio is a mature reflection and fruit of Pope John Paul's experience as he says: «my direct contact with peoples who do not know Christ has convinced me even more of the urgency of missionary activity». Redemptoris Missio offers a fundamental view of the responsibility of the lay faithful in missionary action. Their role in activity of the Church, specially in missionary action today is indispensable. This encyclical thus gives a new dimension to the Christian lay faithful in missionary action. «The church has not been really founded, and is not yet fully alive, nor is it a perfect sign of Christ among men, unless there is a laity worthy of the name working along with the hierarchy. For the Gospel cannot be deeply grounded in the abilities, life and work of any people without the active presence of laymen» (AG, 21).