Church music is a genre of Christian music written for performance in church, or any musical setting of ecclesiastical liturgy, or music set to words expressing propositions of a sacred nature, such as a hymn.

The only record of communal song in the Gospels is the last meeting of the disciples before the Crucifixion:

When they had sung a hymn, they went out into the Mount of Olives.

Outside the Gospels, there is a reference to St. Paul encouraging the Ephesians and Colossians to use psalms, hymns and spiritual songs.

Later, there is a reference in Pliny the Younger who writes to the emperor Trajan (53–117) asking for advice about how to persecute the Christians in Bithynia, and describing their practice of gathering before sunrise and repeating antiphonally "a hymn to Christ, as to God". Antiphonal psalmody is the singing or musical playing of psalms by alternating groups of performers. The peculiar mirror structure of the Hebrew psalms makes it likely that the antiphonal method originated in the services of the ancient Israelites. According to the historian Socrates of Constantinople, 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.

During the first two or three centuries, Christian communities incorporated into their observances features of Greek music and the music of other cultures bordering on the eastern Mediterranean Sea. As the early Church spread from Jerusalem to Asia Minor, North Africa, and Europe, it absorbed other musical influences. For example, the monasteries and churches of Syria were important in the development of psalm singing and the use of strophic devotional song, or hymns. The use of instruments in early Christian music seems to have been frowned upon. In the late 4th or early 5th century, St. Jerome wrote that a Christian maiden ought not even to know what a lyre or flute is like, or to what use it is put. Evidence of musical roles during the 6th through 7th centuries is particularly sparse because of the cycle of invasions of Germanic tribes in the West and doctrinal and political conflict in the East as well as the consequent instability of Christian institutions in the former Roman empire. The introduction of church organ music is traditionally believed to date from the time of the papacy of Pope Vitalian in the 7th century.

Gregorian chant is the main tradition of Western plainchant, a form of monophonic liturgical chant of Western Christianity that accompanied the celebration of Mass and other ritual services. This musical form originated in Monastic life, in which singing the 'Divine Service' nine times a day at the proper hours was upheld according to the Rule of Saint Benedict. Singing psalms made up a large part of the life in a monastic community, while a smaller group and soloists sang the chants.

In its long history, Gregorian Chant has been subjected to many gradual changes and some reforms. It was organized, codified, and notated mainly in the Frankish lands of western and central Europe during the 12th and 13th centuries, with later additions and redactions, but the texts and many of the melodies have antecedents going back several centuries earlier. Although a 9th-century legend credits Pope Gregory the Great with having personally invented Gregorian chant by receiving the chant melodies through divine intervention of the Holy Spirit, scholars now believe that the chant bearing his name arose from a later Carolingian synthesis of Roman and Gallican chant.