The badnjak (Cyrillic: бадњак, Serbian pronunciation: [bǎdɲaːk]), also called veseljak (весељак, [ʋɛˈsɛ̌ʎaːk], literally "jovial one" in Serbian), is a log brought into the house and placed on the fire on the evening of Christmas Eve, a central tradition in Serbian Christmas celebrations much like a yule log in other European traditions. The tree from which the badnjak is cut, preferably a young and straight oak, is ceremonially felled early on the morning of Christmas Eve. The felling, preparation, bringing in, and laying on the fire, are surrounded by elaborate rituals, with many regional variations. The burning of the log is accompanied by prayers that the coming year brings food, happiness, love, luck, and riches. The log burns on throughout Christmas Day, when the first visitor strikes it with a poker or a branch to make sparks fly, while wishing that the family's happiness and prosperity be as abundant as the sparks. As most Serbs today live in towns and cities, the badnjak is often symbolically represented by a cluster of oak twigs with brown leaves attached, with which the home is decorated on Christmas Eve.
Since the early 20th century, the Serbian badnjak tradition has also been celebrated more publicly. Before World War I, soldiers of the Kingdom of Serbia developed the custom of laying a badnjak on a fire in their barracks. In the succeeding Kingdom of Yugoslavia, the military badnjak ceremony was further elaborated and standardized in army service regulations, but the tradition ended at the outbreak of World War II. Since the early 1990s, the Serbian Orthodox Church has, together with local communities, organized public celebrations on Christmas Eve in which the badnjak plays a central role. Parishioners festively cut the sapling to be used as the badnjak and take it to their church, where it is consecrated by a priest before it is ceremonially placed on a fire built in the churchyard.