April Fools' Day is celebrated on April 1st or January 1st. It originated in France on April 1st but most places now celebrate it on January 1st. It is celebrated to poke fun at those who refused to change to the Gregorian calendar and still celebrated New Year's Day on April 1st, seen as silly. On this day, people stick paper fish on others' backs and yell "Poisson d'Avril" when it is discovered, a French prank tradition. While originating in France, many celebrate this day.