monophonic, or unison, chant that accompanies the Latin mass and canonical hours of the Ambrosian rite. The word Ambrosian is derived from St. Ambrose (Ambrose, Saint), bishop of Milan (374–397), from which comes the occasional designation of this rite as Milanese. Despite legends to the contrary, no Ambrosian-chant melodies can be attributed to Ambrose.

The Ambrosian Ordinary (chants of the mass having texts that do not change from day to day) has some relationship to the Roman Gregorian Ordinary (the standard Roman Catholic liturgy and chant): they each have a Kyrie and Gloria, except that the Kyrie is appended to the Ambrosian Gloria (in the Roman Ordinary it precedes the Gloria); each has a Credo (called Symbolum in the Ambrosian rite) and a Sanctus. For the breaking of the Communion breads, the Ambrosian rite uses the Confractorium, a Proper chant (one having a text that varies during the church year), whereas the Gregorian has the Agnus Dei, an Ordinary chant. The Ambrosian Ordinary chants are generally but not always syllabic (one note per syllable). The festive Gloria has expressive melismas (many notes per syllable) at the conclusion of syllabic phrases. Compared to the Gregorian rite, the Ambrosian has few Ordinary chants.

The late date of the Ambrosian-chant manuscripts (12th century) raises doubt concerning the time of the origin of this chant. It is thought that the Ambrosian chant was established and differed stylistically from Gregorian chant in the era of Charlemagne (d. 814), who unsuccessfully endeavoured to replace the Ambrosian with the Gregorian liturgy. Gregorian melodies and texts from this time and later are found integrated within the Ambrosian repertory. Ambrosian chants, however, also include a primitive body of less uniform and theoretically unorganized chants that remained apparently uninfluenced by the polished and systematized Gregorian repertory.

There are several traits native to the Ambrosian chants and not typically Gregorian. Unlike the Gregorian chants (Gregorian chant), the Ambrosian are not stylistically uniform for any liturgical category; e.g., Gregorian Tracts (a category of chant) have certain musical traits in common with each other, but no such consistencies appear among Ambrosian chants. The Ambrosian chants are not written in any mode (theoretical melodic and scale pattern), whereas a given Gregorian chant is in one of the eight church modes. The Ambrosian psalm tones (psalm tone) (formulas for intoning psalms) differ from the Gregorian psalm tones in that the former have no middle cadence (stopping point) and have a greater choice of reciting tones and terminations. Representative of Oriental influence are the Ambrosian melodiae (freely interchangeable melismatic fragments) found in the responsories (a type of chant) for Matins (a service of the canonical hours).