Ever since the 8th century, the Roman Rite of the Catholic Church has celebrated the last seven days of Advent with what are called the "O Antiphons." These verses are traditionally sung during Evening Prayer, but have also been featured in the popular Advent hymn, "O Come, O Come, Emmanuel."
Normally one antiphon is sung per day, from December 17 through December 23. The dates for each antiphon are printed below, as well as a few articles that offer some commentary on the tradition.
December 17: O Sapientia — O Wisdom
December 18: O Adonai — O Lord
December 19: O Radix Jesse — O Root of Jesse
December 20: O Clavis David — O Key of David
December 21: O Oriens — O Dayspring
December 22: O Rex Gentium — O King of the Nations
December 23: O Emmanuel — O God with Us
