American and British English spelling differences are one aspect of American and British English differences.

In the early 18th century, English spelling was not standardized. Differences became noticeable after the publishing of influential dictionaries. Current British English spellings follow, for the most part, those of Samuel Johnson's Dictionary of the English Language (1755). Many of the now characteristic American English spellings were introduced, although for the most part not created, by Noah Webster in his An American Dictionary of the English Language of 1828.

Webster was a strong proponent of spelling reform for reasons both philological and nationalistic. Many spelling changes proposed in the US by Webster himself, and in the early 20th century by the Simplified Spelling Board, never caught on. Among the advocates of spelling reform in England, the influences of those who preferred the Norman (or Anglo-French) spellings of certain words proved decisive. Subsequent spelling adjustments in the UK had little effect on present-day US spelling, and vice versa. While in many cases American English deviated in the 19th century from mainstream British spelling, on the other hand it has also often retained older forms.

The spelling systems of Commonwealth countries, for the most part, closely resemble the British system. In Canada, however, while most spelling is "British", many "American" spellings are also used. Additional information on Canadian and Australian spelling is provided throughout the article.

UK	US	Notes
aeroplane	airplane	Aeroplane, originally a French loanword, is the older spelling. According to the OED, "[a]irplane became the standard U.S. term (replacing aeroplane) after it was adopted by the National Advisory Committee for Aeronautics in 1916. Although A. Lloyd Jones recommended its adoption by the BBC in 1928, it has until recently been no more than an occasional form in British English." In the British National Corpus, aeroplane outnumbers airplane by more than 7:1. The case is similar for UK aerodrome and US airdrome, although both of these forms are now obsolescent. The prefixes aero- and air- both mean air, the first coming from the greek word αÝρας. Thus, for example, the first appears in aeronautics, aerostatics and aerodynamics, and so on, where the second suffix is a greek word, while the second occurs (invariably) in aircraft, airport, airliner, airmail, etc. where the second suffix is an english word. In Canada, Airplane is used more commonly than aeroplane, although aeroplane is not unknown, especially in parts of French Canada (the current French term is, however, avion — aéroplane designating in French the plane ancestor). Both Canada and Australia use aerodrome as a technical term.
aluminium	aluminum	The spelling aluminium is the international standard in the sciences (IUPAC). The American spelling is nonetheless used by many American scientists. Humphry Davy, the element's discoverer, first proposed the name alumium, and then later aluminum. The name aluminium was finally adopted to conform with the -ium ending of metallic elements. Canada as US, Australia as UK.
arse	ass	In vulgar senses "buttocks" ("anus"/"wretch"); unrelated sense "donkey"/"idiot" is ass in both. Both forms are found in Canada and Australia.
barmy	balmy	In sense "slightly insane", "crazy", "foolish", which has limited meaning in American English. Both forms originated in 19th century England from other senses: barmy meant "frothing [as of beer]"; balmy means "warm and soft [as of weather]". British barmy is generally misheard in North America as balmy.
behove	behoove
bogeyman	boogeyman
carburettor	carburetor
charivari	shivaree, charivari	In the US, where both terms are mainly regional, charivari is usually pronounced as shivaree, which is also found in Canada and Cornwall, and is a corruption of the French word.
coupé	coupe	For a two-door car; the horse-drawn carriage is coupé in both; unrelated "cup"/"bowl" is always coupe. In the US, the E is accented when used as a foreign word.
eyrie	aerie	Rhyme with weary and hairy respectively. Both spellings and pronunciations occur in the US.
fillet	fillet, filet	Meat or fish. Pronounced the French way (approximately) in the US, even if the word is spelled fillet.
furore	furor	Furore is a late 18th-century Italian loan that replaced the Latinate form in the UK in the following century, and is usually pronounced with a voiced e. Canada as US, Australia has both.
grotty	grody	Clippings of grotesque; both are slang terms from the 1960s.
haulier	hauler	Haulage contractor; haulier is the older spelling.
moustache	mustache	In the US, according to the Merriam-Webster Collegiate Dictionary and the American Heritage Dictionary, the British spelling is an also-ran, yet the pronunciation with second-syllable stress is a common variant.
mum(my)	mom(my)	Mother. Mom is sporadically regionally found in the UK (West Midlands English); some British dialects have mam, and this is often used in Irish and Welsh English. In the US region of New England, especially in the case of the Boston accent, the British pronunciation of mum is often retained, while it is still spelt mom. Canada has mom and mum; in Australia, mum is used.
naivety	naiveté, naïveté	The American forms are from French, ending [-'eɪ]; the British form is nativised, ending [-i].
pernickety	persnickety	Persnickety is a late 19th-century North American alteration of the Scottish word pernickety.
quin	quint	Abbreviations of quintuplet.
scallywag	scalawag	In the US (where the word originated, as scalawag), scallywag is not unknown.
snigger	snicker	According to major dictionaries, both forms can occur in both dialects, although snigger can cause offense in the US due to the similarity to nigger.
speciality	specialty	In British English the standard usage is speciality, but specialty occurs in the field of medicine, and also as a legal term for a contract under seal. In Canada, specialty prevails; in Australia both are current.
titbit	tidbit