The Trisagion Prayers
Τρισάγιον — Trisagion · tris-AH-gee-on
In brief
The Trisagion Prayers are a short, fixed sequence that opens nearly every Orthodox service and almost every session of private prayer. Prayer books call it the "usual beginning" or "typical beginning." It gathers the whole of prayer into a few lines: it calls on the Holy Spirit, praises the Holy Trinity three times over, asks for mercy, and hands us to the words Christ Himself gave — the Lord's Prayer. Learning it by heart is the first step into Orthodox prayer.
The usual beginning
Open an Orthodox prayer book to the morning prayers, the evening prayers, or almost any service, and the same block of text stands at the head, sometimes just printed as "the usual beginning." It is a doorway everyone walks through: whatever you are about to pray — a prayer rule, an akathist, a memorial — you begin here. Because it is repeated so constantly, most Orthodox Christians know it by heart, and teaching it to a child or a newcomer is where learning to pray begins.
The sequence takes its common name, the Trisagion Prayers, from its central hymn — the Trisagion, Greek for "thrice-holy." That hymn's opening line names God three times as holy, echoing the seraphim in Isaiah's vision who cry "Holy, holy, holy." The whole little office is quietly Trinitarian: it moves from the Spirit, to the thrice-holy God, to the Holy Trinity by name, to the Father's own prayer.
The sequence, line by line
Outside the paschal season the office opens by calling on the Holy Spirit: "O Heavenly King, the Comforter, the Spirit of truth, Who art everywhere and fillest all things; Treasury of blessings and Giver of life: come and abide in us and cleanse us from every impurity, and save our souls, O Good One." (From Pascha to Pentecost this prayer is replaced or omitted, since the Church is then keeping the feast of the Spirit's coming; the prayer returns at Pentecost.) Then comes the Trisagion itself, said three times: "Holy God, Holy Mighty, Holy Immortal, have mercy on us."
There follows the small doxology, "Glory to the Father, and to the Son, and to the Holy Spirit, now and ever and unto ages of ages. Amen," and then the prayer to the Trinity by name: "O Most Holy Trinity, have mercy on us. O Lord, cleanse us from our sins. O Master, pardon our transgressions. O Holy One, visit and heal our infirmities, for Thy Name's sake." "Lord, have mercy" is said three times, the doxology again, and the office ends by handing us to Christ's own words, the Lord's Prayer: "Our Father, Who art in heaven..." In church a priest concludes with the exclamation "For Thine is the Kingdom..."; in private, custom for the ending varies, and a prayer book will show the local usage.
Not the same as the Trisagion Hymn
The words "Holy God, Holy Mighty, Holy Immortal, have mercy on us" also form a hymn sung solemnly at the Divine Liturgy, before the Scripture readings — the Trisagion Hymn, with its own history and ceremonial. The two share the same sacred words but are not the same thing: one is a chanted hymn woven into the public Liturgy, the other is the quiet, spoken opening of personal prayer and of the daily services. When Orthodox Christians speak of "the Trisagion Prayers" or the "usual beginning," they mean this short opening sequence, not the Liturgy's hymn.
For all its brevity, the office is a compact confession of faith. It names each Person of the Holy Trinity, begs mercy in the same breath, and refuses to let prayer become our own performance by ending in words we did not compose. That is why the Church puts it at the threshold of everything: before we ask God for anything, it teaches us whom we are addressing.