A disputed association between April 1 and foolishness is in Geoffrey Chaucer's The Canterbury Tales (1392). In the "Nun's Priest's Tale", a vain cock Chauntecleer is tricked by a fox on Syn March bigan thritty dayes and two. Readers apparently understood this line to mean "32 March", i.e. April 1. However, it is not clear that Chaucer was referencing April 1. Modern scholars believe that there is a copying error in the extant manuscripts and that Chaucer actually wrote, Syn March was gon. If so, the passage would have originally meant 32 days after March, i.e. 2 May, the anniversary of the engagement of King Richard II of England to Anne of Bohemia, which took place in 1381.

In 1508, French poet Eloy d'Amerval referred to a poisson d’avril (April fool, literally "Fish of April"), possibly the first reference to the celebration in France. In the Middle Ages, New Year's Day was celebrated on March 25 in most European towns. In some areas of France, New Year's was a week-long holiday ending on April 1. Some writers suggest that April Fools' originated because those who celebrated on January 1 made fun of those who celebrated on other dates. The use of January 1 as New Year's Day was common in France by the mid-16th century, and this date was adopted officially in 1564 by the Edict of Roussillon.

In 1539, Flemish poet Eduard de Dene wrote of a nobleman who sent his servants on foolish errands on April 1.

In the Netherlands, the origin of April Fools' Day is often attributed to the Dutch victory at Brielle in 1572, where the Spanish Duke Álvarez de Toledo was defeated. "Op 1 april verloor Alva zijn bril" is a Dutch proverb, which can be translated to: "On the first of April, Alva lost his glasses." In this case, the glasses ("bril" in Dutch) serve as a metaphor for Brielle. This theory, however, provides no explanation for the international celebration of April Fools' Day.

In 1686, John Aubrey referred to the celebration as "Fooles holy day", the first British reference. On April 1, 1698, several people were tricked into going to the Tower of London to "see the Lions washed".

Although no Biblical scholar or historian are known to have mentioned a relationship, some have expressed the belief that the origins of April Fool's Day may go back to the Genesis flood narrative. In a 1908 edition of the Harper's Weekly cartoonist Bertha R. McDonald wrote:

Authorities gravely back with it to the time of Noah and the ark. The London Public Advertiser of March 13, 1769, printed: "The mistake of Noah sending the dove out of the ark before the water had abated, on the first day of April, and to perpetuate the memory of this deliverance it was thought proper, whoever forgot so remarkable a circumstance, to punish them by sending them upon some sleeveless errand similar to that ineffectual message upon which the bird was sent by the patriarch".

United Kingdom

In the UK, an April Fool joke is revealed by shouting "April fool!" at the recipient, who becomes the "April fool". A study in the 1950s, by folklorists Iona and Peter Opie, found that in the UK, and in countries whose traditions derived from the UK, the joking ceased at midday. A person playing a joke after midday is the "April fool" themselves.

In Scotland, April Fools' Day was traditionally called 'Huntigowk Day', although this name has fallen into disuse. The name is a corruption of 'Hunt the Gowk', "gowk" being Scots for a cuckoo or a foolish person; alternative terms in Gaelic would be Là na Gocaireachd, 'gowking day', or Là Ruith na Cuthaige, 'the day of running the cuckoo'. The traditional prank is to ask someone to deliver a sealed message that supposedly requests help of some sort. In fact, the message reads "Dinna laugh, dinna smile. Hunt the gowk another mile." The recipient, upon reading it, will explain he can only help if he first contacts another person, and sends the victim to this next person with an identical message, with the same result.

In England a "fool" is known by different names around the country, including a "noodle", "gob", "gobby" or "noddy".

Ireland

In Ireland, it was traditional to entrust the victim with an "important letter" to be given to a named person. That person would then ask the victim to take it to someone else, and so on. The letter when finally opened contained the words "send the fool further".

Prima aprilis in Poland

In Poland, prima aprilis ("1 April" in Latin) as a day of jokes is a centuries-long tradition. It is a day in which many jokes are told; various hoaxes – sometimes very sophisticated – are prepared by people, media (which often cooperate to make the "information" more credible) and even public institutions. Serious activities are usually avoided, and generally every word said on April 1st can be a lie, or a joke. The conviction for this is so strong that the Polish anti-Turkish alliance with Leopold I signed on April 1, 1683, was backdated to March 31. However, for some in Poland prima aprilis ends at noon of April 1st, and prima aprilis jokes after that hour are considered inappropriate and not classy.

Nordic countries

Danes, Finns, Icelanders, Norwegians and Swedes celebrate April Fools' Day (aprilsnar in Danish; aprillipäivä in Finnish). Most news media outlets will publish exactly one false story on April 1; for newspapers this will typically be a first-page article but not the top headline.^[17]

April fish

In Italy, France, Belgium, The Netherlands, and French-speaking areas of Switzerland and Canada, April 1 tradition is often known as "April fish" (poissons d'avril in French, aprilvis in Dutch or pesce d'aprile in Italian). This includes attempting to attach a paper fish to the victim's back without being noticed. Such fish feature prominently on many late 19th- to early 20th-century French April Fools' Day postcards. Many newspapers also spread a false story on April Fools' Day, and a subtle reference to a fish is sometimes given as a clue.^{[citation needed]}

India

In India, there have been numerous references to April Fools' Day in both cinema and popular literature and people are jovially associated with the day. However, this is not any intrinsic part of India's ancient culture.^[18]

Lebanon

In Lebanon, an April Fool joke is revealed by shouting "???? ????? !" (which means "Aprils fool!") at the recipient, who becomes the "April fool".^{[citation needed]}

Spanish-speaking countries

In many Spanish-speaking countries (and the Philippines), "Dia de los Santos Inocentes" (Holy Innocents Day) is celebrated in late December (27, 28 or 29 depending of the denomination, or January 10th for East Syrians), which is very similar to April Fools. Often, people play pranks on each other, trick others, etc.^{[citation needed]}

As well as people playing pranks on one another on April Fools' Day, elaborate practical jokes have appeared on radio and TV stations, newspapers, websites, and have been performed by large corporations. In one famous prank from 1957, the BBC broadcast a film in their Panorama current affairs series purporting to show Swiss farmers picking freshly-grown spaghetti, in what they called the Swiss Spaghetti Harvest. The BBC were later flooded with requests to purchase a spaghetti plant, forcing them to declare the film a hoax on the news the next day.^[19]

With the advent of the Internet and readily available global news services, April Fools' pranks can catch and embarrass a wider audience than ever before.^[20]

December 28, the equivalent day in Spain, Hispanic America and the Philippines, is also the Christian day of celebration of the "Day of the Holy Innocents". The Christian celebration is a holiday in its own right, a religious one, but the tradition of pranks is not, though the latter is observed yearly. After somebody plays a joke or a prank on somebody else, the joker usually cries out, in some regions of Hispanic America: Inocente palomita que te dejaste engañar ("You innocent little dove that let yourself be fooled"), not to be confused with the second translation of palomita, which is popcorn.

In Mexico, the phrase is ¡Inocente para siempre! which means "Innocent forever!". In Argentina, the prankster says ¡Que la inocencia te valga!, which roughly translates as a piece of advice on not to be as gullible as the victim of the prank. In Spain, it is common to say just ¡Inocente! (which in Spanish can mean "Innocent!", but also "Gullible!").^[21]

In Colombia, the term used is "Pásala por Inocentes", which roughly means: "Let it go; today it's Innocent's Day."

In Belgium, this day is also known as the "Day of the innocent children" or "Day of the stupid children". It used to be a day where parents, grandparents, and teachers would fool the children in some way. But the celebration of this day has died out in favor of April Fools' Day.

Nevertheless, on the Spanish island of Menorca, Dia d'enganyar ("Fooling day") is celebrated on April 1 because Menorca was a British possession during part of the 18th century. In Brazil, the "Dia da mentira" ("Day of the lie") is also celebrated on April 1.^[21]

In Iran, on 13th of the first month (Farvardin) of the Iranian calendar (known as Nature's day or Sizdah Be-dar, 1st or 2nd of April), it is common that people spread false news and then shout "Doroughe sizdah" (lie of 13) to the victim. Some of the newspapers and journals also do the same and then somewhere in the bottom of page write "Doroughe sizdah" with inverse letters.^[