"What Child Is This?" is a Christmas carol with lyrics written by William Chatterton Dix in 1865 and set to the tune of "Greensleeves", a traditional English folk song, in 1871. Although written in Great Britain, the carol today is more popular in the United States than its country of origin.

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.