Ambrosian Chant, a method of singing hymns first introduced into the western church by St. Ambrose, about 386. Although generally supposed to be the foundation of all church music, it was in fact derived through the eastern church from the Greeks, and is so little known at this day, that it is impossible to say more of its general character than that it was constructed on the ancient Greek tetra-chords, and embraced the four authentic modes, the four plagal or collateral ones being added by Gregory to form what is known as the Gregorian chant. The Ambrosian chant, and indeed all kinds of church music, were at first limited strictly to the performance of the psalms and doxologies, from an apprehension among the early fathers and bishops that heretical doctrines might creep into the services by the introduction of original hymns. Ambrose, however, in imitation of the Greek fathers, subsequently wrote several hymns, including, it has been erroneously supposed, the Te Deum, which he caused to be habitually sung according to the new method in his church; and St. Augustine, who was baptized there, speaks with great delight of the impression which the performance of the psalms and hymns made upon him.

The Ambrosian chant continued to be used in the services of the church until about the commencement of the 7th century, when it was superseded by the new method adopted by Pope Gregory.