Christmas Carol sheet music is so much a part of our holiday now that we may not think about where it came from or how it's been passed down to us today. The fact is the tradition of carol singing is very old—and not exclusive to Christmas.
The word "carol" is medieval, with roots in both French and Anglo-Normal languages; its original meaning has more to do with dance than Christmas carol sheet music! "Carols" didn't necessarily pertain only to Christmas, or even religious holidays. Over the ages, many "carol" tunes have come down to us that tell other stories in the pattern of verse/refrain (also called "burden"). But while many of us may encounter this type of carol in our musical experience, the odds are we think more of religious expression when we sing carols, as so many of them directly relate the story of Christ's birth.
No one really knows when the first carol was composed, but many musicologists attribute the era of 1350 to 1550 to their initial appearance; religious songs in a verse/refrain format show up as early as the fourteenth century. Most of these carols concerned Christ, the Virgin Mary, or other saints. By the fifteenth century, carols gained status as songs in their own right, an important aspect of medieval music, in some cases with elaborate instrumental and vocal arrangements. These, of course, would have been hand-copied, as music printing was not available yet.
One of these early collections is the Fayrfax Manuscript, a carol songbook specifically for court use that made its appearance toward the end of the 1400s. These carols weren't the earliest form of Christmas carol sheet music, in that their primary theme was the Passion. In fact, it's fortunate that carols survived at all; by the end of the sixteenth century, their popularity waned, no doubt due to the shifting religious sentiments of the era. Carols stayed somewhat "dormant" for two centuries until being revived in the eighteenth century, and this is the era during which many of the carols we know today were composed.
We can thank Gutenberg for rendering us able to enjoy printed music of all kinds today, especially the Christmas carol sheet music we use so much during the holiday season. When you carol, or hear carolers, you're enjoying a Christmas gift that's absolutely free…and spiritually uplifting in the bargain.