Oxford spelling (also Oxford English Dictionary spelling, Oxford style, or Oxford English spelling) is a spelling standard, named after its use by the Oxford University Press, that prescribes the use of British spelling in combination with the suffix -ize in words like realize and organization instead of -ise endings.

Oxford spelling is used by many UK-based academic journals (for example, Nature) and many international organizations (for example, the United Nations and its agencies).^[1][2][3] It is common for academic, formal, and technical writing for an international readership. In digital documents, Oxford spelling may be indicated by the IETF language tag en-GB-oxendict (or historically by en-GB-oed).^[4]

Oxford spelling uses the suffix ‑ize alongside ‑lyse: organization, privatize and recognizable, rather than organisation, privatise and recognisable – alongside analyse, paralyse etc. The Oxford University Press states that the belief that ‑ize is an exclusively North American variant is incorrect.^[5] The Oxford spelling affects about 200 verbs,^[6] and is favoured on etymological grounds, in that ‑ize corresponds more closely to the Greek root of most ‑ize verbs, -ίζω (‑ízō).^[7]

The suffix ‑ize has been in use in the UK since the 15th century,^[5] and is the spelling variation used in North American English. The OED lists the ‑ise form of words separately, as "a frequent spelling of ‑IZE ...":

This practice probably began first in French; in modern French the suffix has become ‑iser, alike in words from Greek, as baptiser, évangéliser, organiser, and those formed after them from Latin, as civiliser, cicatriser, humaniser.

Hence, some have used the spelling ‑ise in English, as in French, for all these words, and some prefer ‑ise in words formed in French or English from Latin elements, retaining ‑ize for those formed from Greek elements.

However, the suffix itself, whatever the element to which it is added, is in its origin the Greek ‑ιζειν, Latin ‑izāre; and, as the pronunciation is also with z, there is no reason why in English the special French spelling should be followed, in opposition to that which is at once etymological and phonetic. In this Dictionary the termination is uniformly written ‑ize. (In the Greek ‑ιζ‑, the i was short, so originally in Latin, but the double consonant z (= dz, ts) made the syllable long; when the z became a simple consonant, /‑idz/ became īz, whence English /‑aɪz/.)

The Oxford use of ‑ize does not extend to the spelling of words not traced to the Greek ‑izo, ‑izein suffixes. One group of such words is those ending in ‑lyse, such as analyse, paralyse and catalyse, which come from the Greek verb λύω, lyo, the perfective (aorist) stem of which is ‑lys-: for these, ‑lyse is the more etymological spelling. Others include advertise, arise, compromise, chastise, disguise, improvise, prise (in the sense of open), and televise.^{[additional citation(s) needed][8]}

In addition to the OUP's "Oxford"-branded dictionaries, other British dictionary publishers that list ‑ize suffixes first include Cassell, Collins, and Longman.^[9]

Oxford spelling is used by the Oxford University Press (OUP) for British publications,^[10] including its Oxford English Dictionary (OED) and its influential British style guide Hart's Rules, and by other publishers who are "etymology conscious", according to Merriam-Webster.^[11]

Oxford spelling (especially the first form listed in the Concise Oxford English Dictionary, Twelfth Edition) is the official or de facto spelling standard used in style guides of the international organizations that belong to the United Nations System.^[2] This includes the World Health Organization, the International Telecommunication Union, the International Labour Organization, the World Food Programme, the International Court of Justice, and UNESCO, and all UN treaties and declarations, such as the Universal Declaration of Human Rights.^[12]

Other international organizations that adhere to this standard include the International Organization for Standardization (ISO), the International Electrotechnical Commission (IEC), the World Trade Organization (WTO), the North Atlantic Treaty Organization (NATO), the International Atomic Energy Agency (IAEA), Interpol, the International Committee of the Red Cross (ICRC), the World Wide Fund for Nature (WWF), Amnesty International (AI), the World Economic Forum (WEF) and the Global Biodiversity Information Facility (GBIF).^[12][13]

Oxford spelling is used in a number of academic publications, including the London-based scientific journal Nature and all other UK-based "Nature"-branded journals, the Philosophical Transactions of the Royal Society, and the Journal of Physiology. It is used by The Times Literary Supplement, Encyclopædia Britannica and Cambridge University Press.^[12] Newspapers and magazines in the UK normally use -ise. The style guide of The Times recommended -ize until 1992, when it switched to -ise.^[8] The newspaper's chief revise editor, Richard Dixon, wrote of the change:^[8]

In the great -ize versus -ise debate, The Times has opted latterly for simplicity over a sort of erudition ... But in the Style Guide of 1992, the following entry appeared: "-ise, -isation: avoid the z construction in almost all cases. This is volcanic ground, with common usage straining the crust of classical etymology. This guidance is a revision of the Greek zeta root ending in the direction of a Latin ending and common usage: apologise, organise, emphasise, televise, circumcise. The only truly awkward result is capsize, which should be left in its Grecian peace."

In both the King James Bible and the works of Shakespeare, -ize endings are used throughout.^{[additional citation(s) needed]} Well-known literary works that use Oxford spelling include The Lord of the Rings by J. R. R. Tolkien (an Oxford University professor), And Then There Were None by Agatha Christie (married to an All Souls archaeologist), and The Lion, the Witch and the Wardrobe by C. S. Lewis (a fellow of Magdalen College, Oxford).

Oxford spelling is not necessarily followed by the staff of the University of Oxford. The university's style guide, last updated in 2016, recommended the use of -ise for internal use.^[14]

The following table summarizes a few general spelling differences among five major English spelling conventions, plus the French spelling convention for comparison. Note: en-GB simply stands for British English; it is not specified whether -ize or -ise should be used. The language tag en-GB-oxendict, however, demands the use of -ize and -ization.

• Canadian English spelling
• Macquarie Dictionary (Australian usage)
• Oxford comma
• Spelling differences: -ise, -ize

• The Oxford English Dictionary (1st ed.)
• The Oxford English Dictionary 2nd ed. (20 vols.)
• The Oxford English Dictionary, Oxford: Oxford University Press (latest edition: on WWW)

• IANA Language Tag Registration Form for en-GB-oed
• AskOxford: Are spellings like privatize and organize Americanisms?
• British Medical Journal: -ize right
• World Wide Words: The endings "-ise" and "-ize"
• Detailed blog post about -ise and -ize verbs in British English.
• Tieken-Boon Van Ostade, Ingrid. An Introduction to Late Modern English. Edinburgh University Press, 2009, p. 38.