April Fools' Day, also known as All Fools' Day is not a national holiday, but its traditions are observed in many countries on 1 April.
The day is observed by trying to play a practical joke on a victim who becomes known as an April Fool. The practical jokes range from simple to elaborate. Whatever the trick, the prankster usually ends it by yelling to his victim, "April Fool!"
In certain countries, April Fools' jokes must be made before noon on 1 April otherwise the tables are reversed and it is the prankster who is the April Fool.
The origin of the customs of the day are shrouded in mystery. Some scholars believe it is likely to be a relic of festivities held to mark the vernal equinox. These celebrations of the first days of spring, began on 25 March, and ended on 2 April. Certainly there is some evidence to suggest that 1 April was observed as a general festival in pagan Britain.
More commonly, the customs are associated with the switch to the Gregorian calendar in France during the sixteenth century.
Historically, many parts of the world, celebrated 1 April as New Year's Day - due to its relationship with the start of Spring.
France was one of the first countries to adopt 1 January as their official New Year's Day, by decree of Charles IX in 1564. This was before the 1582 adoption of the Gregorian calendar.
The gifts and traditions which had been the feature of the 1st of April switched to January 1st. However, many people either refused to accept the change or did not hear about the news several years. Those who still celebrated April 1 were seen as 'fools' by the general populace, and fair game to be the butt of pranks and tricks were known as a "poisson d'avril" or "April fish."
The traditions spread to England and Scotland in the eighteenth century, and was brought to the American colonies by both the English and French.
In France the April fool is known as 'poisson d'avril' (April fish). It is not known what exactly the fish refers to, but it may be related to the sun leaving Pieces (the fish) at the start of April. A part of the tradition in France was the placing of dead fish unknowingly on the backs of friends. Today, real fish have been replaced with fish-shaped paper shapes that children try to sneak onto the back of their friends' shirts. Shops and bakeries also offer special fish-shaped sweets.
Mexico's equivalent to April Fool's Day is on December 28th. Originally, the day was a sombre remembrance of the slaughter of the innocent children by King Herod, though over the years, it has evolved into a light-hearted commemoration involving pranks and tricks.
The Dutch have separate reasons for celebrating the 1st of April. In 1572, the Netherlands were under Spanish rule. On 1 April 1572 Dutch rebels seized the town of Den Briel. This marked the start of the general civil rising against the Spanish across the Netherlands. The Duke of Alba was the commander of the Spanish army at the time, and he could not prevent the uprising from gathering momentum. 'Bril' is the Dutch word for glasses, so it was said that "Alba lost his glasses." The Dutch commemorate this with jokes and humour on the first of April.
In Scotland, April Fool's Day is celebrated over two days. Called Taily Day, The second day is devoted to pranks involving the buttocks. The "kick me" sign can be traced back to Taily Day.
Some April Fool's Day videos from Google, BMW and the BBC.