From the Latin for "holy," a hymn of adoration and praise which begins, "Holy, holy, holy, Lord God of Hosts." It typically follows the preface in the eucharistic prayer (BCP, pp. 334, 341, 362, 367, 371, 373, 402, 404). It is sung or said by the celebrant and people. The Sanctus is based on the song of the seraphim as recorded in Isaiah's vision of the Lord in the year King Uzziah died (Is 6:1-3; see Rv 4:8). The congregation may be said to share in the praise of God that is continually offered by the whole company of heaven. The Sanctus has been accompanied by bells since the fifteenth century in some places.
Glossary definitions provided courtesy of Church Publishing Incorporated, New York, NY,(All Rights reserved) from "An Episcopal Dictionary of the Church, A User Friendly Reference for Episcopalians," Don S. Armentrout and Robert Boak Slocum, editors.