The living, teaching office of the Church, whose task it is to give an authentic interpretation of the word of God, whether in its written form (Sacred Scripture) or in the form of Tradition. The Magisterium ensures the Church's fidelity to the teaching of the Apostles in matters of faith and morals.
CCC 85 "The task of giving an authentic interpretation of the Word of God, whether in its written form or in the form of Tradition, has been entrusted to the living, teaching office of the Church alone. Its authority in this matter is exercised in the name of Jesus Christ. This means that the task of interpretation has been entrusted to the bishops in communion with the successor of Peter, the Bishop of Rome."
CCC 86 "Yet this Magisterium is not superior to the Word of God, but is its servant. It teaches only what has been handed on to it. At the divine command and with the help of the Holy Spirit, it listens to this devotedly, guards it with dedication, and expounds it faithfully. All that it proposes for belief as being divinely revealed is drawn from this single deposit of faith."
CCC 890 "The mission of the Magisterium is linked to the definitive nature of the covenant established by God with his people in Christ. It is this Magisterium's task to preserve God's people from deviations and defections and to guarantee them the objective possibility of professing the true faith without error. Thus, the pastoral duty of the Magisterium is aimed at seeing to it that the People of God abides in the truth that liberates. To fulfill this service, Christ endowed the Church's shepherds with the charism of infallibility in matters of faith and morals. The exercise of this charism has several forms."
CCC 891 "The Roman Pontiff, head of the college of bishops, enjoys this infallibility in virtue of his office when, as supreme pastor and teacher of all the faithful -- who confirms his brethren in the faith -- he proclaims by a definitive act a doctrine pertaining to faith or morals ... The infallibility promised to the Church is also present in the body of bishops when, together with Peter's sucessor, they exercise the supreme Magisterium, above all in an Ecumenical Council. When the Church through its supreme Magisterium proposes a doctrine for belief as being divinely revealed, and as the teaching of Christ, the definitions must be adhered to with the obedience of faith. This infallibility extends as far as the deposit of divine Revelation itself.
CCC 892 "Divine assistance is also given to the successors of the apostles, teaching in communion with the successor of Peter, and, in a particular way, to the bishop of Rome, pastor of the whole Church, when, without arriving at an infallible definition and without pronouncing in a definitive manner, they propose in the exercise of the ordinary Magisterium a teaching that leads to better understanding of Revelation in matters of faith and morals. To this ordinary teaching the faithful are to adhere to it with religious assent which, though distinct from the assent of faith, is nonetheless an extension of it.
CCC 2033 "The Magisterium of the Pastors of the Church in moral matters is ordinarily exercised in catechesis and preaching, with the help of the works of theologians and spiritual authors. Thus from generation to generation, under the aegis and vigilance of the pastors, the deposit of Christian moral teaching has been handed on, a deposit composed of a characteristic body of rules, commandments, and virtues proceeding from faith in Christ and animated by charity. Alongside the Creed and the Our Father, the basis for this catechesis has traditionally been the Decalogue which sets out the principles of moral life valid for all men."