Christian commemoration of the occasion upon which Jesus Christ took three of his disciples, Peter, James, and John, up on a mountain, where Moses and Elijah appeared and Jesus was transfigured, his face and clothes becoming white and shining as light (Mark 9:2–13; Matthew 17:1–13; Luke 9:28–36). The festival celebrates the revelation of the eternal glory of the Second Person of the Trinity, which was normally veiled during Christ's life on earth. According to tradition, the event took place on Mt. Tabor. (Tabor, Mount)

It is not known when the festival was first celebrated, but it was kept in Jerusalem as early as the 7th century and in most parts of the Byzantine Empire by the 9th century. It was gradually introduced into the Western Church, and its observance was fixed as August 6 by Pope Callistus III in 1457, as a thank offering for the victory over the Turks at Belgrade on Aug. 6, 1456.

In the Orthodox Church it has always been a major festival. In some churches it is celebrated on other dates. The Syrians and Armenians keep it on the seventh Sunday after Pentecost and some Lutherans on the last Sunday after Epiphany.