An antiphon (Greek ἀντίφωνον, ἀντί "opposite" + φωνή "voice") is a response, usually sung in Gregorian chant, to a psalm or some other part of a religious service, such as at Vespers or at a Mass. This meaning gave rise to the antiphony style of singing, see call and response.
A piece of music which is performed by two semi-independent choirs interacting with one another, often singing alternate musical phrases, is known as antiphonal. In particular, antiphonal psalmody is the singing or musical playing of psalms by alternating groups of performers. The peculiar mirror structure of the Hebrew psalms renders it probable that the antiphonal method originated in the services of the ancient Israelites. According to the historian Socrates, its introduction into Christian worship was due to Ignatius of Antioch (died 107), who in a vision had seen the angels singing in alternate choirs. In the Latin Church it was not practised until more than two centuries later, when it was introduced by Ambrose, bishop of Milan, who compiled an antiphonary, or collection of works suitable for antiphonal singing (also known as an antiphonal). The antiphonary still in use in the Roman Roman Catholic Church was compiled by Gregory the Great (590).
When two or more groups of singers sing in alternation the style of music can also be called polychoral. Specifically, this term is usually applied to music of the late Renaissance and early Baroque. Polychoral techniques are a definitive characteristic of the music of the Venetian school, exemplified by the works of Giovanni Gabrieli; this music is often known as the Venetian polychoral style. The Venetian polychoral style was an important innovation of the late Renaissance, and this style, with its variations as it spread across Europe after 1600, helps to define the beginning of the Baroque era. Polychoral music was not limited to Italy in the Renaissance; it was popular in Spain and Germany, and there are examples from the 19th and 20th centuries, from composers as diverse as Hector Berlioz, Igor Stravinsky and Karlheinz Stockhausen.