Plainchant, or plainsong, is unaccompanied singing of Christan liturgies, which began in the 13th centuries. The term is derived from the Latin cantus planus (plain song). It is often used in a more restricted sense, referring to the Roman Catholic Church's sung liturgy, Gregorian chant, which is misattributed to Pope Gregory (540–604). The plainchant repertoire was refined, particularly following the Council of Trent (1545–1563), when it was standardized in order to create a common liturgical practice. Centuries later, the Second Vatican Council of 1963 replaced Latin with vernacular languages, and introduced new liturgical music


The standardization of the Roman Catholic Church's liturgical materials as an aid to expansion was instrumental in the development of musical notation, although this was not recognized as an important consequence in early medieval sources. Dating from the 9th century, the early notation of chant, with neumes representing notes or groups of notes, would gradually develop into the highly precise system of symbols for pitch, rhythm, and dynamics used today. Notation was crucial to the expansion of composition from a single melodic line to polyphony, and in medieval times plainchant melodies were someimes elaborated into complex polyphonic compositions.


While plainchant has been of enormous importance to the church through the centuries, and remains so, it reached a general audience during the mid-1990s with the release of the album Chant by The Benedictine Monks of Santo Domingo de Silos, who sold three million copies in the United States. The popularity of the plainchant-like works of Hildegard von Bingen (1098–1179) has also helped plainchant to become a vehicle for new-age aesthetics, and to generate an interest in other historical female composers.