The Magisterium is the teaching authority of the Catholic Church, exercised by the Pope and the bishops in communion with him. Catholics believe that Christ entrusted the apostles — and their successors — with the authority to teach, sanctify, and govern in His name (Matthew 28:18-20). The Magisterium operates at two levels: (1) The Extraordinary Magisterium — infallible teachings proclaimed through ecumenical councils or ex cathedra papal declarations (e.g., the Immaculate Conception, the Assumption). (2) The Ordinary Magisterium — the day-to-day teaching of the Pope and bishops through encyclicals, pastoral letters, catechesis, and preaching. Even non-infallible ordinary teaching requires the religious assent of the faithful. The Magisterium is guided by the Holy Spirit, ensuring that the Church does not err in matters of faith and morals. It interprets both Sacred Scripture and Sacred Tradition, which together form the single deposit of faith. This three-legged stool of Scripture, Tradition, and Magisterium distinguishes Catholic authority from the Protestant principle of sola Scriptura.