A king cake, also known as a three kings cake or a baby cake, is a cake associated in many countries with Epiphany, the celebration of the Twelfth Night after Christmas. Traditionally made with brioche dough, in most cases a fève (lit. 'fava bean') such as a figurine representing the Christ Child, was hidden inside. After the cake is cut, whoever finds the fève in their slice wins a prize. In a nod to tradition, a plastic baby figurine is often taped to the packaging of commercially produced cakes. Modern fèves can be made of other materials, but always represent the King or Baby Jesus.

The origin of the cake tradition was popularly believed to be related to the Roman Saturnalia. These were festivals dedicated to the god Saturn so that the Roman people, in general could celebrate the longer days that began to come after the winter solstice. For this reason, Margaret Hasluck disputed the Greek tradition commemorating St. Basil's feast day with vasilopita, claiming that both customs had a common origin in the Saturnalia and Kronia.

In the Middle Ages, it was said that the king who was chosen had to pay the assembly a general round of drinks. To prevent cheating, the edible bean was replaced by a porcelain bean. In Christian tradition the cake commemorates the witness of the "Three Kings".

The earliest known reference to a king cake in North America, including a recipe, dates to 1649. An early French settler of Port Royal, Acadia (now Annapolis Royal, Nova Scotia) was required to deliver annually to the lord of Port Royal and his wife, "on the eve of the Feast of Kings ... a round cake made with a quarter bushel of the finest white wheat flour, kneaded with six eggs and half a pound of the freshest butter, with a black bean placed in the cake’s edge ... to their château and seigneurial manor at Port Royal."

The tradition of the Mardi Gras king cake did not become established until the 20th-century, although the ubiquitous gold, purple and green sprinkles have been standard decoration since 1872. The cake is usually purchased at a shop. Many holiday foods have rituals and customs connected to the preparation of the food, but the customs of the kings cake mainly revolve around the fève. Sugar was always a big industry in New Orleans, where local bakeries took an active role in turning the cake into a modern cultural icon. Old-fashioned versions of the cake are basically a round braided brioche without filling but these days bakeries try to outdo one another with creative fillings.

There are two different versions of the French king cake: the galette and the gâteau. The galette des rois is a flaky puff pastry traditionally filled with frangipane. These days the filling may also be fruit, chocolate or cream-based fillings. It has become a tradition for pastry chefs to create innovative versions of the galette featuring ingredients like flavored liquors, candied fruits and ganache.

The gâteau des rois associated mainly with the region of Provence in the south of France is a brioche dough decorated with candied fruit and coarse sugar.

The Guianan galette (more commonly known as the Creole galette) is a traditional pastry of French Guianan cuisine. This is a Creole variant of the galette des rois which is eaten as a dessert during Epiphany. It can be garnished with cream, coconut, guava, etc. It is consumed throughout the Carnival period (from the Epiphany until Lent, ending Ash Wednesday) and preferably accompanied by champagne.^{[citation needed]}