The earliest Roman Sacramentaries are the first complete sources for the Roman Rite. These were written in the Latin language which had gradually replaced Greek as the language of the Roman liturgy. Scholars differ as to the precise time when the transition was complete, giving dates from the second half of the third century up to the end of the fourth. Both languages must have been used side by side during a fairly long period of transition. The genius of the Latin language certainly affected the ethos of the Roman Rite. Latin is naturally terse and austere when compared with the rhetorical abundance of Greek. (F127) It was a natural tendency of Latin to curtail redundant phrases, and this terseness and austerity are a noticeable mark of the Roman Mass.

Of the Sacramentaries, three stand out as the earliest, the most complete, the most important in every way. These are the so­called Leonine, Gelasian, and Gregorian Sacramentaries, named respectively after three popes St. Leo (440-61), Gelasius (492-6), and St. Gregory the Great (590-604). The names imply an authorship which cannot be substantiated even in the case of St. Gregory. There is no evidence that Pope Gelasius contributed anything to the Sacramentary attributed to him; St. Leo may have composed some of the prayers in the Leonine Sacramentary, but this is not certain; but the Gregorian Sacramentary almost certainly contains some material composed by St. Gregory. The Leonine Sacramentary, the Sacramentarium Leonianum, the oldest of the three, can be found in a seventh century manuscript preserved in the Chapter Library at Verona. The Sacramentary had been preceded by what were known as Libelli Missarum. They were small books containing the formularies for parts of the Mass for the Church in a particular diocese or locality, but not the Canon which was fixed, the readings, or the sung parts. They provided the intermediary between extempore celebrations and the fixed formularies of the Sacramentary. No actual examples are known to have survived, but the certainty of their existence is known through literary references, and above all through the Leonine Sacramentary which consists of a collection of Libelli. Unfortunately the collection is not complete, and lacks both the Order and the Canon of the Mass, but it contains many Mass propers which can still be found in the Roman Missal.

The Gelasian Sacramentary is the oldest Roman Massbook in the proper sense of the term. It is far more complete than the Leonine, and has the feasts arranged according to the Ecclesiastical Year. It also contains the Canon and several votive Masses. The most ancient extant manuscript dates from the 8th century and contains some Gallican material.