The " O! Antiphons " were first used by the Church in the 8th and 9th centuries. They are based on various titles used for the Christ and are scripturally-based short prayers used from the 17th to the 23rd of December. In the Roman Catholic Church they are the antiphons for the Vespers in the Office of the Day. In these "O Antiphons" the Church expresses her deep longing for the coming of the Messiah.

The Advent hymn "O Come, O Come, Emmanuel" --- a personal favorite of mine --- is based on the "O Antiphons" and was written sometime during the 9th Century. The hymn , as can be seen below, begins with the last antiphon. I have adapted the antiphons to a Chaplet for Advent.

A SEASON OF HOPE – Rediscovering Our Advent Heritage

by the Brotherhood of Hope is a delightful combination of hymns, chant, gospel, and contemporary songs.

Prayers

Beginning on the Medal:
Jesus, our Lord, save me from my sins. Come, protect me from all dangers and lead me to salvation.

On the large beads, consider the meditation (using either antiphon or verse ) and pray the Our Father .

On the small beads, pray Hail Mary (three for each meditation).

At the conclusion: 
Come, Lord Jesus, do not delay; give new courage to Your people who trust in Your love. By Your coming, raise us to the joy of Your Kingdom, where you live and reign with the Father and the Holy Spirit, one God, forever. Amen

The Antiphons

O WISDOM, who came from the mouth of the Most High, reaching from end to end and ordering all things mightily and sweetly:
COME , and teach us the way of prudence. Amen. "O Sapientia..."

December 18

O LORD AND RULER of the House of Israel, who appeared to Moses in the flame of the burning bush and gave him the law on Sinai:
COME , and redeem us with outstretched arms. Amen. "O Adonai..."

December 19

O ROOT OF JESSE, that stands for an ensign of the people, before whom the kings keep silence and unto whom the Gentiles shall make supplication:
COME , to deliver us, and tarry not. Amen. "O Radix Jesse..."

December 20

O KEY OF DAVID, and Sceptre of the House of Israel, who opens and no man shuts, who shuts and no man opens:
COME , and bring forth the captive from his prison, he who sits in darkness and in the shadow of death. Amen. "O Clavis David..."

December 21

O DAWN OF THE EAST, brightness of light eternal, and Sun of Justice:
COME , and enlighten those who sit in darkness and in the shadow of death. Amen. "O Oriens..."

December 22

O KING OF THE GENTILES and their desired One, the Cornerstone that makes both one:
COME , and deliver man, whom you formed out of the dust of the earth. Amen. "O Rex..."

December 23

O EMMANUEL, God with us, Our King and Lawgiver, the expected of the nations and their Saviour:
COME to save us, O Lord our God. Amen. "O Emmanuel..."

Hymn

What is an Antiphon?

From the Marian Libary :

Michel Huglo in The New Grove Dictionary of Music and Musicians gives the definition of antiphon: "In Latin Christian chant generally, a liturgical chant with a prose text, sung in association with a psalm" ... "derived from the classical Greek antiphonis ('resonating with')": "And in later Christian texts, the term' antiphonia' was used to mean 'antiphony', or psalmody sung by two choirs, perhaps to distinguish it from responsorial psalmody, performed by a soloist." It was used in early Christianity as a type of liturgical worship, as is documented in Theodore of Mopsuestia (d 428), and even as early as Ambrose (d. 397) who wrote antiphons and hymns. (p. 472)

Antiphona generally precede short chants, with texts averaging between ten and 25 words and simple melodies. "Several categories of antiphon developed without any link with psalmody, such as the great processional antiphons of the Gregorian processional." (p. 472, Part V) Although antiphons normally have biblical texts, these four processional antiphons express instead the devotion of the people (p. 472).

"The composers of the antiphon melodies, like all composers of chant, borrowed the elements of their compositions from pre-existing models, and did not seek originality. The models themselves seem to have been fixed in the second half of the 8thcentury for Gregorian chant." (p. 473). If we were thus able to trace the antiphons to their earliest possible origin, the models for them were probably fixed in this time period.

The Marian antiphons have been sung, since the 13th century, at the close of Compline, the last Office of the liturgical day; they occur in groups in antiphoners and processionals, usually together with the Proper of the Assumption (15 August). They comprise a group from the early repertory of antiphons (especially those for Christmas).