Benedicamus Domino (Latin: "Let us bless the Lord") is a closing salutation that was formerly used in the Latin Mass instead of the Ite, missa est in Masses which lack the Gloria (i.e., Masses of the season during Advent, Septuagesima, Lent, and Passiontide; ferial Masses per annum at which the Mass of the preceding Sunday was repeated, except in Eastertide; most votive Masses). The response, said afterwards, is Deo gratias ("Thanks be to God"). It is also sung as a versicle at the end of all Offices.
See also: Mass ordinary § VI. Ite, missa est
Apparently the chant was unknown in Rome before about AD 1000, and may have originated in the Gallican liturgy. In modern chantbooks, the music given for the chant is exactly the same as for the Ite missa est, but it is not known how much that was true in the medieval period as well.
The text was frequently troped, especially by adding text between the two words, or using the melody as the cantus firmus for an organum. The use of this chant as a tenor was common in the St. Martial and Notre Dame schools of polyphony, including a dozen settings in the Magnus Liber Organi.
During the liturgical reforms of Pope Pius XII (1938–1958) and Pope John XXIII (1958–1963) the use of the Benedicamus Domino was much restricted. By 1963, it was only recited or chanted when an exposition immediately follows the Mass (Eucharisticum Mysterium, 120). It is rarely heard in Anglo-Saxon countries, processions being rarities there. It is still however, used in the Divine Office.
Lutherans continue to use it in the Divine Office and at the end of their Divine Service.
Some orders of traditionalist Catholics continue to use the pre-1955 liturgical books without the permission of the Holy See, such as the Society of Saint Pius V (SSPV), the Institute of the Mother of Good Counsel (IMBC), and Bp. Donald J. Sanborn's Roman Catholic Institute (RCI), and thus use the Benedicamus Domino in the traditional manner.
Mario Giuseppe Genesi, "Un Benedicamus Domino congetturalmente bivocale dei secc. XII-XIII nei Codici Bobbiesi: considerazioni a latere e comparazioni repertoriali";sta in "Archivum Bobiense",Rivista degli Archivi Storici della Città di Bobbio, 2007/2008, pp. 201–394.