Preferred variants

In both British English and American English, many words have variant spellings, but most of the time one variant is preferred over the other. In dictionaries, the preferred spelling is listed first among the headwords of an entry. Examples follow:

• acknowledgement vs acknowledgment: acknowledgement is preferred in British English,^[9] acknowledgment in American English.
• judgement vs judgment: judgement is preferred in British English (except in the sense of a judge's decision, in which case judgment is preferred), judgment in American English.
• per cent vs percent: per cent is preferred in British English, percent in American English.
• dialogue vs dialog: In a non-technical context, the spelling dialogue is preferred in American English. In Webster's dictionary, dialogue is given first, and Chambers also indicates dialog is less used in North America.^[10]
• catalogue vs catalog: Webster's treats this case differently, as does Chambers^[11]—catalog is the preferred spelling in American English.
• glamour vs glamor: The spelling glamour is preferred in both British and American English. (Glamourous is sometimes found in American English, but is usually considered incorrect in British English, where glamorous is the only accepted form.)
• foetus vs fetus: In American English, foetus is never used. In British English, usage is divided. In academic literature, fetus is preferred.
• aluminium vs aluminum: aluminum is the prevalent spelling throughout North America; however, in scientific literature aluminium should be used, as recommended by the International Union of Pure and Applied Chemistry, or IUPAC. (The two spellings also have different pronunciations.)
  
• sulphur vs sulfur: sulphur is the prevalent spelling outside North America; however, in scientific literature sulfur should be used, as recommended by IUPAC. (see Sulfur#Spelling and etymology)
  
• caesium vs cesium: cesium is the prevalent spelling throughout North America; however, in scientific literature caesium should be used, as recommended by IUPAC.
  

Archaic spelling

Older sources use many archaic variants (such as shew for show), which are not to be used outside quotations except in special circumstances (for example, quire may be used instead of choir in architectural contexts).

When archaic spelling is used in the title of a work, modernize the spelling in the text of the article but retain the original spelling in the references. For example, the text of an article might read "Thomas Ady attacked the Demonology of King James..." while the citation should read Daemonologie, In Forme of a Dialogie, Diuided into three Bookes. By James Rx, 1597....". Adding a <!-- comment --> may help prevent well-meaning editors from correcting the spelling "mistakes".

As per WP:Manual of Style § Quotations, archaic glyphs should be modernized, including within quotations and titles (e.g., æ→ae, œ→oe, ſ→s, and y^e→the). Archaic spellings (including capitalization, punctuation, and emphasis that would be non-standard today) are retained in quotations, and we rarely need to provide any translations into Modern English if the source material is Elizabethan or later. For Middle English, treat it on a case-by-case basis, but always provide translation for Old English.

Different spellings, different meanings

Several words change their meaning when spelt differently.

• cheque – check: to check is to ensure; outside the US, a bill of exchange drawn on a bank payable on demand is a cheque.
• kerb – curb: In British English, kerb is the edge of the road or pavement (UK) where kerbstones can be found. In the US, it is spelled curb, and may be attached to a sidewalk. To curb is to limit or control in either dialect.
• disc – disk: Outside of computing, in British English the usual spelling is disc (meaning a thin flat circular object); in American English disk and disc are normally interchangeable. However, in computing (in both British & American English), disk usually refers to magnetic disks, as in hard disk drives, dating back to the first magnetic disks used by US-developed mainframe computers. Disc usually refers to optical discs, beginning with the Compact Disc (developed outside the US) and continuing with DVD (the last "D" of the acronym usually meaning disc regardless of its uncertain etymology), Blu-ray Disc, and even defunct formats such as HD DVD.
• draught – draft: In the UK draft is a preliminary version of a document, while draught is a drink or a current of air; all are usually spelled draft in the US, but draught has been making a comeback in reference to beverages.
• enquiry – inquiry: for most British writers, an enquiry is a request for information, but an inquiry is a formal investigation.
• ensure – insure: To ensure is to make sure. In British English, to insure is to take out an insurance policy. In American English, to insure is sometimes used instead of to ensure.^[12][13]
• judgement – judgment: In Australian and British law, a judge's decision in a case is always spelt judgment. On the other hand, the forming of opinion or conclusion by an ordinary person is usually spelt judgement.
• metre – meter: in most countries other than the US, metre is the metric unit of length, and meter is a measuring device; in these dialects metre is also the rhythm of a line of verse, but the word as part of the technical name of a given metre (pentameter, hexameter, etc.) is spelled -meter.
• programme – program: In British English, the spelling program can be used for computer program. In all other cases, programme is invariably used.
• storey – story: a story is a tale; outside of the US, upper floors of buildings are spelt storey.^[14]
• theatre – theater: Many uses of either spelling can be found in American English. Both theater and theatre are commonly used among theatre professionals. The spelling theatre can be seen in names like the Kodak Theatre and AMC Theatres. However, the spelling theater is used for the various venues at the John F. Kennedy Center for the Performing Arts, and all major American newspapers, such as The New York Times's theater section^[15] to refer to both the dramatic arts as well as to the buildings where performances take place. The Columbia University Guide to Standard American English states that theater is used except in proper names.^[16]
• tyre – tire: In American and Canadian English, tire is used to refer to fatigue and the inflated rim of a wheel. In British and other forms of English, tire means "to fatigue" and tyre is the inflated rim of a wheel.

British English with "-ise"

Spellings: centre, programme, labour, defence, organisation; recognise, advise, devise, advertise, and analyse
Language tag (a code identifying the language used): en-GB.

Examples of organizations adhering to this standard: European Union (EU), Organisation for Economic Co-operation and Development (OECD), Commonwealth Secretariat (Commonwealth of Nations), African Union (AU), Organisation of Eastern Caribbean States (OECS), International Olympic Committee (IOC), UK Armed Forces and Ministry of Defence, Fédération Internationale de Football Association (FIFA). The UK government does not seem to have an official position on spelling, though it often uses this variant in communications.

Major publications: BBC, The Economist, Financial Times, The Guardian, The Lancet, New Scientist, The Times.

British English with "-ize" (Oxford spelling)

Spellings: centre, programme, labour, defence, organization; recognize, but: advise, devise, advertise, and analyse
Language tag: en-GB-oxendict

Oxford spelling is based on the Oxford English Dictionary,^[17] and followed by Collins^[18] and Cassell's^[19] dictionaries, whereas Chambers lists both ‑ize and ‑ise for British English.^[20] The Concise Oxford English Dictionary notes that "the form ize has been in use in English since the 16th century. The alternative spelling ise (reflecting a French influence) is in common use, especially in British English".^[21]

Examples of organizations adhering to this standard: United Nations organizations (UN, WHO, UNESCO, UNICEF, ITU, ILO, etc.), World Trade Organization (WTO), International Organization for Standardization (ISO), International Electrotechnical Commission (IEC), International Atomic Energy Agency (IAEA), Organization of the Petroleum Exporting Countries (OPEC), South Asian Association for Regional Cooperation (SAARC), International Criminal Police Organization (Interpol), International Committee of the Red Cross (ICRC), World Wide Fund for Nature (WWF), Amnesty International, World Economic Forum, and the North Atlantic Treaty Organization (NATO).

Major publications: Encyclopædia Britannica (despite being an American publication since 1911), Nature, The Times Literary Supplement.

American English

Spellings: center, program, labor, defense, organization; recognize, but: advise, devise, advertise, and analyze
Language tag: en-US

Examples of organizations adhering to this standard: International Monetary Fund, World Bank, Organization of American States, NAFTA Secretariat.

Major publications: International New York Times, Newsweek, The New York Times, Science, Scientific American, Time, The Wall Street Journal.