The origin of this custom are complex and a matter of much debate. It is likely a relic of the once common festivities held on the vernal equinox, which began on the 25th of March, old new year´s day, and ended on the 2nd of April.Though the 1st of April appears to have been observed as a general festival in Britain in antiquity, it was apparently not until the beginning of the 1700´s that the making of April-fools was a common custom. In Scotland the custom was known as "hunting the gowk," i.e. the cuckoo, and April-fools were "April-gowks," the cuckoo being a term of contempt, as it is in many countries.One of the earliest connections of the day with fools is Chaucer´s story the nun´s priest´s tale (c.1400), which concerns two fools and takes place "thritty dayes and two" from the beginning of March, which is April. The significance of this is difficult to determine.

Europe may have derived its April-fooling from the French. French and Dutch references from 1508 and 1539 respectively describe April Fools' Day jokes and the custom of making them on the first of April. France was one of the first nations to make January officially New Years´day (which was already celebrated by many), by decree of Charles XI. This was in 1564, even before the 1582 adoption of the Gregorian calendar (See Julian start of the year). Thus the New Years gifts and visits of felicitation which had been the feature of the 1st of April became associated with the first day of January, and those who disliked or did not hear about the change were fair game for those wits who amused themselves by sending mock presents and paying calls of pretended ceremony on the 1st of April. In France the person fooled is known as poisson d'avril. This has been explained as arising from the fact that in April the sun quits the zodiacal sign of the fish. The French traditionally celebrated this holiday by placing dead fish on the backs of friends. Today the fish has been replaced with paper cut-out.The Dutch celebrate the 1st of April for other reasons. In 1572, the Netherlands were ruled by Spain's King Philip II. Roaming the region were Dutch rebels who called themselves Geuzen, after the French "gueux," meaning beggars. On April 1, 1572, the Geuzen seized the small coastal town of Den Briel. This event was also the start of the general civil rising against the Spanish in other cities in the Netherlands. The Duke of Alba, commander of the Spanish army could not prevent the uprising. Bril is the Dutch word for glasses, so on April 1, 1572, "Alba lost his glasses." The Dutch commemorate this with humour on the first of April.
 
Well-Known Hoaxes
 
Alabama Changes the Value of Pi.
The April 1998 newsletter of New Mexicans for Science and Reason contained an article written by physicist Mark Boslough claiming that the Alabama Legislature had voted to change the value of the mathematical constant pi to the "Biblical value" of 3.0. This claim originally appeared as a news story in the 1961 science fiction novel Stranger in a Strange Land by Robert A. Heinlein.
 
Spaghetti Trees
The BBC television programme Panorama ran a famous hoax in 1957, showing the Swiss harvesting spaghetti from trees. They had claimed that the despised pest the spaghetti weevil had been eradicated. A large number of people contacted the BBC wanting to know how to cultivate their own spaghetti trees. It was in fact filmed in St. Albans.
 
Left Handed Whoppers
In 1998, Burger King ran an ad in USA Today, saying that people could get a Whopper for left-handed people whose condiments were designed to drip out of the right side.
 
Taco Liberty Bell
In 1996, Taco Bell took out a full-page advertisement in The New York Time announcing that they had purchased the Liberty Bell to "reduce the country's debt" and renamed it the "Taco Liberty Bell." When asked about the sale, White House press secretary Mike McCurry replied tongue-in-cheek that the Lincoln Memorial had also been sold and would henceforth be known as the Ford Lincoln Mercury Memorial.
 
Real News on April Fools' Day.
The frequency of April Fool hoaxes sometimes makes people doubt real news stories released on 1 April.
 
April Fool Day
 
Residents running from an approaching tsunami in Hilo, Hawaii
 

The 1 April 1946 Aleutian Island earthquake tsunami that killed 165 people on Hawaii and Alaska resulted in the creation of a tsunami warning system (specifically the Pacific Tsunami Warning Centre), established in 1949 for Pacific Ocean area countries. The tsunami in question is known in Hawaii as the "April Fools' Day Tsunami" due to people drowning due to thinking the warnings were an April Fools' prank.
 
The 2005 death of comedian Mitch Hedberg was originally dismissed as an April Fools' joke. The comedian's March 29, 2005 death was announced on April 1, 2005.
 
Gmail's April 2004 launch was widely believed to be a prank, as Google was known to include joke pages on their website, until that point. However, the introduction of the Paper Archive option on April 1, 2007 is a Gmail hoax. Gmail Paper is a supposed service for Google to send users paper copies of their messages.
 
The merger of Square and its rival company, Enix, took place on April 1, 2003, and was originally thought to be a joke. Fans of the long running Square series Final Fantasy often claim that the merger was in fact a joke, claiming that series has declined after the merger. People obeying hoax messages to telephone fictitious people such as "Mr. C. Lion" and "Mr. L. E. Fant" at a telephone number that turns out to be a zoo, sometimes cause a serious overload to zoos' telephone switchboards.
 
The announcement of the anime version of the Powerpuff Girls, Demashita! Powerpuff Girls Z, was on April Fools Day causing many to think it was a joke.

The upcoming game Mario & Sonic at the Olympic Games was announced only a couple days before April Fools Day so many thought that Mario and Sonic together for the very first time was a joke.
 
On April 1, 2007, employees at Google's New York City office were alerted that a ball python kept in an engineer's cubicle had escaped and was on the loose. An internal e-mail acknowledged that "the timing...could not be more awkward" but that the escaped snake was in fact an actual occurrence and not a prank.