This appendix explains the Catholic Church’s Magisterium, its official teaching authority entrusted to the Pope and the bishops as successors to the Apostles. This authority serves to authentically interpret and safeguard the Word of God found in Scripture and Tradition. The appendix traces its historical development from Christ’s commissioning of the Apostles, through early Church councils and the definitions of the Councils of Trent and Vatican I, which clarified papal infallibility. A crucial point is that not all Magisterial documents carry the same weight. A hierarchy of authority exists, ranging from infallible dogmas requiring the assent of faith, to definitive teachings that must be firmly held, to the authoritative but non-infallible teachings found in documents like encyclicals, which require a religious submission of intellect and will. This structure ensures clarity on how different teachings guide the faith and life of the Church.