All Fools’ Day, April 1 is not a national holiday, but is widely recognized and celebrated as a day where many people play all kinds of jokes and foolishness. The day is marked by the commission of good humoured or funny jokes, hoaxes, and other practical jokes of varying sophistication on friends, family members, teachers, neighbors, work associates, etc.
The earliest recorded association between April 1 and foolishness can be found in Chaucer’s Canterbury Tales (1392). Many writers suggest that the restoration of January 1 as New Year’s Day in the 16th century was responsible for the creation of the holiday, but this theory does not explain earlier references. In Chaucer’s Canterbury Tales (1392), the “Nun’s Priest’s Tale” is set Syn March bigan thritty dayes and two. Modern scholars believe that there is a copying error in the extant manuscripts and that Chaucer actually wrote, Syn March was gon. Thus the passage originally meant 32 days after March, i.e. May 2, the anniversary of the engagement of King Richard II of England to Anne of Bohemia, which took place in 1381. However, readers apparently misunderstood this line to mean “32nd of March,” i.e. 1st April. In Chaucer’s tale, the vain cock Chauntecleer is tricked by a fox. (excerpt from wikipedia)