Novus Ordo Missae

The "Novus Ordo Missae" (New Order of the Mass) is the form of the Roman Catholic Mass introduced by Pope Paul VI in 1969 after the Second Vatican Council, replacing the Tridentine Mass (from the Tridentine Missal promulgated by the Quo Primum bull (1570) of Pope Pius V following the Council of Trent). The revised Roman Missal approved by Pope Paul VI and introducing the reforms was written by a team of experts, led by Archbishop Annibale Bugnini, after the end of the Council. With the new Mass, the priest now faces the congregation rather than the altar; certain changes to the altar and sanctuary were made; and the new Mass allows, but does not encourage or discourage, the use of vernacular translations (i.e. translations in the local common language). When the vernacular is used, it is still recommended that at least some of the Mass be conducted in Latin and Gregorian chant.

A number of Traditional Catholics, such as those of Una Voce, the Society of St. Pius X, or followers of Sedevacantism, believe that the Mass according to the new Roman Missal goes against the bulls of previous popes and so contains changes that they would regard as dangerous to the faith. Others link the decline of the Church to the "collapse" of the liturgy. Their views are however in a minority within Catholicism. Most Catholics now attend Mass under the Pauline rite, while church altars have been adapted in conformity with the Decree of Sacrosanctam Concilium. Sacrosanctam Concilium requires the official language of the Mass remains Latin. However, Latin is now rarely used in any church ceremonial.

In the early 2000s it was announced that the Tridentine Mass could once again on occasions be celebrated in St. Peter's Basilica, though not on the main altar.