The Mass is the central liturgical service of the Eucharist in the Catholic Church, in which bread and wine are consecrated and become the body and blood of Christ. As defined by the Church at the Council of Trent, in the Mass "the same Christ who offered himself once in a bloody manner on the altar of the cross, is present and offered in an unbloody manner". The Church describes the Mass as the "source and summit of the Christian life", and teaches that the Mass is a sacrifice, in which the sacramental bread and wine, through consecration by an ordained priest, become the sacrificial body, blood, soul, and divinity of Christ as the sacrifice on Calvary made truly present once again on the altar. The Catholic Church permits only baptised members in the state of grace to receive Christ in the Eucharist.

The Catholic Church, also known as the Roman Catholic Church, is the largest Christian church, with 1.39 billion baptized Catholics worldwide as of 2022. It is among the world's oldest and largest international institutions, and has played a prominent role in the history and development of Western civilization. The church consists of 24 sui iuris churches, including the Latin Church and 23 Eastern Catholic Churches, which comprise almost 3,500 dioceses and eparchies located around the world. The pope, who is the bishop of Rome, is the chief pastor of the church. The Diocese of Rome, known as the Holy See, is the central governing authority of the church. The administrative body of the Holy See, the Roman Curia, has its principal offices in Vatican City, a small independent city-state and enclave within the Italian capital city of Rome, of which the pope is head of state.