A Christmas carol is a carol (a song or hymn) on the theme of Christmas, traditionally sung at Christmas itself or during the surrounding Christmas and holiday season. The term noel has sometimes been used, especially for carols of French origin. Christmas carols may be regarded as a subset of the broader category of Christmas music.

The first known Christmas hymns may be traced to 4th-century Rome. Latin hymns such as Veni redemptor gentium, written by Ambrose, Archbishop of Milan, were austere statements of the theological doctrine of the Incarnation in opposition to Arianism. Corde natus ex Parentis (Of the Father's heart begotten) by the Spanish poet Prudentius (d. 413) is still sung in some churches today.

In the 9th and 10th centuries, the Christmas sequence (or prose) was introduced in Northern European monasteries, developing under Bernard of Clairvaux into a sequence of rhymed stanzas. In the 12th century the Parisian monk Adam of Saint Victor began to derive music from popular songs, introducing something closer to the traditional Christmas carol.

In the 13th century, in France, Germany, and particularly, Italy, under the influence of Francis of Assisi, a strong tradition of popular Christmas songs in regional native languages developed. Christmas carols in English first appear in a 1426 work of John Awdlay, a Shropshire chaplain, who lists twenty five "caroles of Cristemas", probably sung by groups of 'wassailers', who went from house to house. The songs now known specifically as carols were originally communal songs sung during celebrations like harvest tide as well as Christmas. It was only later that carols began to be sung in church, and to be specifically associated with Christmas.

Many carols which have gained popularity were printed in Piae Cantiones, a collection of late medieval Latin songs which was first published in 1582. Early, Latin forms of carols such as "Christ was born on Christmas Day", "Good Christian Men, Rejoice" and "Good King Wenceslas" can be found in this book. "Adeste Fideles" ("O Come all ye faithful") appears in its current form in the mid-18th century, although the words may have originated in the 13th century. The origin of the tune is disputed.

Carols gained in popularity after the Reformation in the countries where Protestant churches gained prominence (as well-known Reformers like Martin Luther authored carols and encouraged their use in worship). This was a consequence of the fact that the Lutheran reformation warmly welcomed music. During the years that the Puritan ban on Christmas was in place in England, semi-clandestine religious services marking Christ's birth continued to be held, and people sang carols in secret.

The publication of Christmas music books in the 19th century helped to widen the popular appeal of carols. "God Rest Ye Merry, Gentlemen", "The First Noel", "I Saw Three Ships" and "Hark! The Herald Angels Sing" appear in English antiquarian William Sandys' 1833 collection Christmas Carols, Ancient and Modern. Composers such as Arthur Sullivan helped to repopularise the carol, and it is this period that gave rise to such favourites as "Good King Wenceslas" and "It Came Upon the Midnight Clear", a New England carol written by Edmund H. Sears and Richard S. Willis. The publication in 1871 of Christmas Carols, New and Old by Henry Ramsden Bramley and Sir John Stainer was a significant contribution to a revival of carols in Victorian Britain. In 1916, Charles Lewis Hutchins published Carols Old and Carols New, a scholarly collection which suffered from a short print run and is consequently rarely available today. The Oxford Book of Carols, first published in 1928 by Oxford University Press (OUP), was a notably successful collection; edited by the British composers Martin Shaw and Ralph Vaughan Williams, along with clergyman and author Percy Dearmer, it became a widely used source of carols in among choirs and church congregations in Britain and remains in print today.

The singing of carols was further popularised in the 20th century when OUP published one of the most popular carol books in the English-speaking world, Carols for Choirs. First published in 1961 and edited by David Willcocks and Reginald Jacques, this bestselling series has since expanded to a five-volume set. Along with editor John Rutter, the compilers included many arrangements of carols derived from sources such as Piae Cantiones, as well as pieces by modern composers such as William Walton, Benjamin Britten, Richard Rodney Bennett, William Mathias and John Rutter.