Trisagion Hymn

The Trisagion sometimes called by its opening line Agios O Theos, is a standard hymn of the Divine Liturgy in most of the Eastern Orthodox, Oriental Orthodox and Eastern Catholic churches. The Latin name Tersanctus or Ter Sanctus is sometimes used to refer to this hymn, although this name is also sometimes used to refer to the Sanctus; it is the latter, a different formula, which is used in Western Christianity in the Mass.

In churches which use the Byzantine Rite, the Trisagion is chanted immediately before the Prokeimenon and the Epistle reading. It is also included in a set of prayers named for it, called the Trisagion Prayers, which forms part of numerous services (the Hours, Vespers, Matins, and as part of the opening prayers for most services).

In the Latin Church, the main regular use of the Trisagion is on Good Friday, when it is sung throughout the ceremony of the Adoration of the Cross.