The Tridentine calendar is the calendar of saints to be honoured in the course of the liturgical year in the official liturgy of the Roman Rite as reformed by Pope Pius V, implementing a decision of the Council of Trent, which entrusted the task to the Pope. The text of the Tridentine calendar can be found in the original editions of the Tridentine Roman Breviary and of the Tridentine Roman Missal. Use of both these texts, which included Pius V's revised calendar, was made obligatory throughout the Latin Church except where other texts of at least two centuries' antiquity were in use, and departures from it were not allowed. The Apostolic Constitution Quod a nobis, which imposed use of the Tridentine Roman Breviary, and the corresponding Apostolic Constitution Quo primum concerning the Tridentine Roman Missal both decreed: "No one whosoever is permitted to alter this letter or heedlessly to venture to go contrary to this notice of Our permission, statute, ordinance, command, precept, grant, indult, declaration, will, decree and prohibition. Should anyone, however, presume to commit such an act, he should know that he will incur the wrath of Almighty God and of the Blessed Apostles Peter and Paul."

Later editions of the Roman calendar

Soon after the publication of this 1907 table, Pope Pius X made a general revision of the rubrics of the calendar, the result of which (with a few additions by Pope Pius XI) can be seen in General Roman Calendar of 1954. This was followed by Pope Pius XII's simplifying revision of 1955 (see General Roman Calendar of Pope Pius XII). John XXIII's General Roman Calendar of 1960 reduced the number of celebrations and completely abandoned the ranking as Doubles, Simples, etc. The General Roman Calendar of 1969 has subsequent adjustments and is currently in general use in the Latin Church (the present General Roman Calendar, observed for instance by the Pope himself).

The Tridentine calendar

January

February

In leap years, a day is added and it is of 29 days but the Feast of St. Matthias is celebrated on the 25th day and then is said twice Sexto Kalendas, that is on the 24th and 25th day, and thus the Dominical letter is changed to the one above, that if it be B, into A, if it be C, into B, similarly also in the others.

March

April

May

June

July

August

September

October

November

December