April Fools' Day is celebrated in many countries on April 1 every year. Sometimes referred to as All Fools' Day, April 1 is not a national holiday, but is widely recognized and celebrated as a day when people play practical jokes and hoaxes on each other.
In Italy, France and Belgium, children and adults traditionally tack paper fishes on each other's back as a trick and shout "April fish!" in their local languages (pesce d'aprile!, poisson d'avril! and aprilvis! in Italian, French and Flemish, respectively). Such fish feature prominently on many French late 19th to early 20th century April Fools' Day postcards.
The earliest recorded association between April 1 and foolishness is an ambiguous reference in Chaucer's Canterbury Tales (1392). Many writers suggest that the restoration of January 1 by Pope Gregory XIII as New Year's Day of the Gregorian Calendar in the 16th century was responsible for the creation of the holiday, sometimes questioned for earlier references.