DEO GRATIAS. - A formula of greeting and thanksgiving already used by s. Paolo (I Cor., 15, 52; II Cor., 2, 14). S. Agostino speaks of it as a distinctive expression for the Christians of Africa, or as a greeting, and explains it (Enarr. in Ps., n. 6): « Fratres, cum vident homines, D. g. dicunt... Num enim non est locus gratulationis, quando se invicem vident qui habitant in Christo? ».
In liturgical worship the faithful say this formula in response to the Benedicamus Domino; in the Roman and Ambrosian Mass after the Ite Missa est, in the Gallican and Mozarabic liturgy after the announcement of the title of a Lesson, and in the Divine Office after all the Lessons, formerly also after the reading of the Acts of the Martyrs, in order to thank the Lord for the instruction received from the divine word or for the encouragement to perform good works. On Holy Saturday the celebrant says it after announcing the Easter chant of the Alleluia. The bishop says it at the presentation of candidates for the diaconate and priesthood, after having assured himself of their worthiness, and at the consecration of bishops and abbots, when they have taken the prescribed oath of fidelity. Formerly, the supreme pontiff said it on the day of the Resurrection, after having heard the number of the newly baptized (Ordo Romanus I, 3), etc.