The most solemn service of the Roman Catholic Church, representing the commemoration and mystical repetition of the Last Supper. The name is derived from the words, "Ite, missa est (congregatio)" -- literally, "Depart, the congregation is dismissed" -- sung at the end of the service.

The Mass consists of a number of items whose texts vary from day to day (Proper, proprium missae) and others having the same text in every Mass (Ordinary, ordinarium missae). Another classification can be made according to whether an item is 1) recited on a monotone or spoken, or 2) sung to a distinct melody. The recitation is entrusted to the celebrant priest and his assistants, the other to the choir (schola).

The following shows the normal structure of the Mass:

For each item of the Ordinary there exist numerous melodies (e.g., about 300 for the Agnus Dei), the earliest of which date from the 11th century.

Requiem Mass

A musical setting of the Mass for the Dead(Missa pro defunctis), so called because it begins with the Introit "Requiem aeternam dona eis Domine" (Give them eternal rest, O Lord). The liturgical structure of this Mass is essentially like that of any other Mass, except that the joyful portions of the Ordinary (Gloria and Credo) are omitted and the Alleluia is replaced by a Tract, after which the sequence "Dies irae" is added.

Plainsong Mass

The polyphonic setting of a Gregorian Mass Ordinary, with each movement drawing its musical material from the corresponding item of the plainsong Mass.  Such a Mass is cyclical from the liturgical point of view, since it fully corresponds to one of the plainsong cycles, each of which is assigned to a specific liturgical situation.

Cantus Firmus Mass

This is a Mass in which all the movements are based on one and the same melody, usually in the tenor.  This cyclical type is perhaps the most common of all between 1400 and 1600.  According to the source of the "cantus firmus,"  three species can be distinguished:  Masses based on 1) a liturgical, 2) a secular, and 3) an invented "cantus firmus."

Paraphrase Mass

In this version, the melodic lines paraphrase the original cantus firmus.  Generally, the first four or five notes of the cantus firmus, on the original pitch, are used to begin the melodic lines of the mass.

Parody Mass

Term for an important practice in the 15th- and 16th-century Mass composition, i.e., incorporating into the Mass material derived from various voice-parts or from entire sections of a polyphonic composition such as motet, chanson, madrigal.  This extensive borrowing distinguishes the parody Mass from the Cantus Firmus Mass, which employs only one voice-part (tenor or superius) of its model.  Whereas in the Cantus Firmus Masses there is a fairly uniform practice of employing the borrowed melody as the tenor of each Mass item, in the parody Masses a large variety of methods is used, in regard to both the amount and the treatment of the borrowed material.  The 16th-century Parody Mass incorporates not fragments taken from individual parts but entire polyphonic segments of the model, in this period usually a motet.