"O Come, All Ye Faithful", also known as "Adeste Fideles", is a Christmas carol that has been attributed to various authors, including John Francis Wade (1711–1786), John Reading (1645–1692), King John IV of Portugal (1604–1656), and anonymous Cistercian monks. The earliest printed version is in a book published by Wade. A manuscript by Wade, dating to 1751, is held by Stonyhurst College in Lancashire.

A Christmas carol is a carol on the theme of Christmas, traditionally sung at Christmas itself or during the surrounding Christmas 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.