O come, O come, Emmanuel is the mid-19th century translation by John Mason Neale and Henry Sloane Coffin of the Ecclesiastical Latin text "Veni, veni, Emmanuel".
This is the harmonization from A Students' Hymnal,
ed. Walford Davies
The melody has been used by many composers, including Respighi in his Trittico Botticelliano, and contemporary composers James Macmillan and Arvo Part