The Yule log, Yule clog, or Christmas block is a specially selected log burnt on a hearth as a winter tradition in regions of Europe, and subsequently North America. The origin of the folk custom is unclear. Like other traditions associated with Yule (such as the Yule boar), the custom may ultimately derive from Proto-Indo-European religion as similar traditions have been recorded in Celtic, Germanic, Baltic and Slavic paganism, among others.

American folklorist Linda Watts provides the following overview of the custom:

The familiar custom of burning the Yule log dates back to earlier solstice celebrations and the tradition of bonfires. The Christmas practice calls for burning a portion of the log each evening until Twelfth Night (January 6). The log is subsequently placed beneath the bed for luck, and particularly for protection from the household threats of lightning and, with some irony, fire. Many have beliefs based on the yule log as it burns, and by counting the sparks and such, they seek to discern their fortunes for the new year and beyond.

Watts notes that the Yule log is one of various "emblem[s] of divine light" that feature in winter holiday customs (other examples include the Yule fire and Yule candle).