In Western Christianity, the Sanctus is sung (or said) as the final words of the Preface of the Eucharistic Prayer, the prayer of consecration of the bread and wine. The preface, which alters according to the season, usually concludes with words describing the praise of the worshippers joining with the angels, who are pictured as praising God with the words of the Sanctus:
The first part of the Sanctus is adapted from , which describes the prophet Isaiah's vision of the throne of God surrounded by six-winged, ministering seraphim. A similar representation may be found in . In Jewish liturgy, the verse from Isaiah is uttered by the congregation during Kedusha, a prayer said during the cantor's repetition of the Amidah (18 Benedictions):
The Sanctus has been set to several plainchant melodies, of which one is given in the Roman Missal, and many composers have set it to more complex music. It constitutes a mandatory part of any mass setting.
In the Tridentine Mass the priest joins his hands while saying the word "Sanctus" and then, bowing, continues to recite the whole of the Sanctus in a lower voice, while a small bell is rung; then, on reaching the words "Benedictus qui venit in nomine Domini", he stands erect again and makes the Sign of the Cross. He then continues immediately with the Canon of the Mass, while the choir, if there is one, sings the Sanctus, pausing for the Consecration and continuing with the Benedictus part afterwards.
As a result of this division, the Sanctus has sometimes been referred to as the Sanctus-Benedictus.
In the Mass as revised after the Second Vatican Council, the only ceremony prescribed for the priest is to join his hands. He and the people sing or recite together the whole of the Sanctus, before the priest begins the Eucharistic Prayer.
1973 International Commission on English in the Liturgy English version
English version often found in earlier hand missals
Note that the Sanctus should not be confused with the Trisagion.