This has got to be one of the oldest carols still sung today. Dating back to 12th century, it's considered a folk song, a carol, and a children's hymn. By the 13th century the melody was sung during the Fete de l’Ane (Festival of the Donkey), the focus of which was the flight into Egypt by the holy family. During the mass for this festival, a donkey was often led or ridden into the church.
The song has become popular in the U.S. since 1920, when it was translated into English by Robert Davis. Its been recorded by many artists, including Harry Belafonte, Garth Brooks, Johnny Cash, Tennesee Ernie Ford, Burl Ives, the Louvin Brothers, and Peter, Paul, and Mary.