Missale Romanum is the incipit of the apostolic constitution of 3 April 1969 by which Pope Paul VI promulgated the revised rite of Mass, setting the first Sunday of Advent at the end of that year as the date on which it would enter into force. The revised Missal itself was not published until the following year, and full vernacular translations appeared much later.
The document made particular mention of the following significant changes from the previous edition of the Roman Missal, most of which had been introduced on a provisional basis in the immediately preceding years:
- To the single Canon of the previous edition (which, with minor alterations, was preserved as the "First Eucharistic Prayer or Roman Canon") were added three alternative Eucharistic Prayers, and the number of prefaces was increased.
- The rites of the Ordinary of the Mass (in Latin, Ordo Missae) - that is, the largely unvarying part of the liturgy - were "simplified, due care being taken to preserve their substance". "Elements that, with the passage of time, came to be duplicated or were added with but little advantage" were eliminated, especially in the rites for the presentation of the bread and wine, the breaking of the bread, and communion.
- "'Other elements that have suffered injury through accident of history' are restored 'to the tradition of the Fathers' (SC art. 50), for example, the homily (see SC art. 52), the general intercessions or prayer of the faithful (see SC art. 53), and the penitential rite or act of reconciliation with God and the community at the beginning of the Mass."
- The proportion of the Bible read at Mass was greatly increased. Prior to the reforms of Pius XII (which reduced the proportions further), 1% of the Old Testament and 16.5% of the New Testament had been read at Mass. Since 1970, the equivalent proportions for Sundays and weekdays (leaving aside major feasts) have been 13.5% of the Old Testament and 71.5% of the New Testament. This was made possible through an increase in the number of readings at Mass and the introduction of a three-year cycle of readings on Sundays and a two-year cycle on weekdays.
In addition to these changes, the document noted that the revision considerably modified other sections of the Missal, such as the Proper of Seasons, the Proper of Saints, the Common of Saints, the Ritual Masses and the Votive Masses, adding that "[the] number [of the prayers] has been increased, so that the new forms might better correspond to new needs, and the text of older prayers has been restored on the basis of the ancient sources".