A réveillon (French: [ʁevɛjɔ̃] (listen)) is a long dinner held in the evening preceding Christmas Day and New Year's Eve. Its name descends from the word réveil (meaning "waking"), because participation involves staying awake until morning, as the meal finishes.

The practice is observed in Belgium, France, Brazil, Romania in the Canadian provinces of Quebec, Manitoba, Ontario, Alberta and New Brunswick, the city of New Orleans, and some other French-speaking places. In Portuguese-speaking countries, it is also a designation for the party preceding New Year's Day. In the United States, the réveillon tradition is still observed in New Orleans due to the city's strong French-Creole heritage, with a number of the city's restaurants offering special réveillon menus on Christmas Eve. It is also observed by many Franco-American families throughout New England.

The term is first documented in 18th-century France, and was used by the French as a name for the night-long party dinners held by the nobility. Eventually the word began to be used by other courts (amongst them the Portuguese courts) and after the French Revolution it was adopted as a definition of the New Year's Eve.