The Gloria in Excelsis Deo, glory to God in the highest, is the greater doxology, sung near the beginning of the Mass on Sundays and feasts and pointedly omitted in the penitential seasons of Advent and Lent, so that its return at Christmas and Easter is felt as a release. It opens with the words the angels sing to the shepherds in Luke's Gospel and continues into an early liturgical composition of praise addressed to God the Father and to Christ the Lamb, one of the psalmi idiotici, the freely composed hymns that the early church set alongside the biblical psalms.
Its Greek form is attested by the fourth century, as a morning hymn, before it settled into its place in the Western Mass. The hymn is essentially jubilant: it is praise for its own sake, with only a brief petition, and its structure of stacked acclamations, we praise you, we bless you, we adore you, we glorify you, gives it a rising, celebratory character that has drawn composers from plainchant through the great polyphonic and orchestral Mass settings. Its seasonal suppression and restoration make it, within the liturgical year, one of the clearest markers of the difference between fasting and feasting.
The hymn's Latin text was fixed by the early medieval period, but restrictions on who could sing it, originally reserved to bishops and later extended to priests only on specific occasions, loosened over centuries until it became a normal part of the Sunday and festal Mass for any priest to intone, a liturgical history that traces the wider medieval pattern of practices once limited to bishops becoming general parish use.