Chances are you probably know this song as "Carol of the Bells," but that is an adaptation of an older Ukrainian carol "Shchedryk," or "The Little Swallow."
"The Little Swallow" is actually more of a New Year's carol, as the original lyrics don't reference Christmas at all and it pre-dates the arrival of Christianity in Ukraine. They tell of a swallow that enters a household and tells the occupant of good fortune that will find him in the coming year.
The tune was later adapted in the early 20th century by Ukrainian composer Mykola Leontovych and lyrics added by Peter J. Wilhousky for the familiar "Carol of the Bells."
In the performance below, Ukrainian-British singer-songwriter Katie Melua is joined by the Gori Women's Choir for a performance of "The Little Swallow" with the original Ukranian lyrics.