Some cited sources:

• William Studwell, The Christmas Carol Reader (New York: Harrington Park Press, 1995)
• Erik Routley, The English Carol (New York: Oxford University Press, 1959).
• Dearmer, Percy., R. Vaughan Williams, Martin Shaw, eds., The Oxford Book of Carols (Oxford: Oxford University Press, 1928).
• The Shorter New Oxford Book of Carols (Oxford: Oxford University Press, 1993)
• The Penguin Book of Christmas Carols (London: Penguin, 1965)
• William L. Simon, ed., The Reader's Digest Merry Christmas Songbook (Pleasantville, NY: Readers Digest Association, revised 2003).
• Ian Bradley, The Penguin Book of Carols (London: Penguin, 1999)