Gregorian chant, also known as plainchant or old Roman chant, is the official music of the Western Roman liturgy. The Church considers it to be the sung rather than spoken prayer, i.e., not an aesthetic vehicle to support the liturgy, but rather liturgy itself. Gregorian chant features a) an unaccompanied—a cappella—sacred, single melodic line (monophonic texture), b) a mainly smooth, step-wise melodic motion with narrow range, c) free rhythm, and d) Latin texts mainly derived from the Bible, particularly the Book of Psalms. Music in early Roman Catholic Church services was confined to vocal music, i.e., no instruments, and its function was strictly limited to teaching religious doctrine to the common people. It was widely believed that the social hierarchy (class system) upheld by the Church was the reflection of a preordained, natural, and unquestionable order. Gregorian chant, with its unaccompanied single-line, static melodies, was the perfect sound picture of that balance and order. These one-line musical structures form the basis for the ritual of the Mass, and continued to be mandated in the Catholic Mass up until the 20th century.

Pope Gregory I, also known as Pope Gregory "The Great," is often given credit for creating Gregorian chant. However, most modern music historians believe that plainsong evolved slowly over the preceding centuries, gradually incorporating musical traits from different cultures. It is nonetheless likely that Pope Gregory played an important part in regulating and organizing the musical aspects of the Mass, which contained Gregorian chant.

The meditative, soothing, and otherworldly qualities of Gregorian chant have appealed to listeners throughout the ages. In 1994, a recording made by the Benedictine monks at the Monastery of Santo Domingo de Silos in Spain sold more than two million copies to become the fastest, best-selling “classical” record up until that point.