Rex is a New Orleans Carnival Krewe which stages one of the city's most celebrated parades on Mardi Gras Day. Rex is Latin for "King", and Rex reigns as "The King of Carnival".

A krewe is a social organization that stages parades and/or balls for the Carnival season. The term is best known for its association with Mardi Gras celebrations in New Orleans, but is also used in other Carnival celebrations throughout Louisiana and along the Gulf of Mexico, such as the Gasparilla Pirate Festival in Tampa, Florida, Springtime Tallahassee, and Krewe of Amalee in DeLand, Florida with the Mardi Gras on Mainstreet Parade as well as in La Crosse, Wisconsin and at the Saint Paul Winter Carnival.