Acronyms and initialisms

Acronyms and initialisms both consist of a string of letters that are the first letters of each word of the title or phrase they refer to. Each letter is usually capitalised. The term acronym is often used to cover both acronyms and initialisms, but there is a difference between them.

The letters of an acronym can be pronounced as a single word:

The letters of an initialism are pronounced one by one, as separate syllables:

A few of these shortened forms may be pronounced either way – for example, WHO (World Health Organization). They may thus be treated as either acronyms or initialisms.

Shortened forms that have the same spelling as normal words (e.g. WHO, POW, PIN) can raise accessibility issues because of the way they are treated by screen readers. For web writing, it is a good idea to define terms on every webpage because of this issue.

Neither acronyms nor initialisms are punctuated with full stops. Add an s, without an apostrophe, for acronyms and initialisms that take a plural:

Using acronyms and initialisms

Before an acronym or initialism is used in the text, give the full title or phrase, followed by the shortened form in brackets. After this, use the shortened form only, unless there is a good reason to repeat the full title or phrase in a new section or chapter – for example, if many pages separate the previous use of the shortened form from the next.

As a general rule, if an acronym or initialism would be used just once or twice in the text, write the term in full rather than introducing the shortened form.

Capitalisation of acronyms and initialisms

The names of organisations take capital letters in both their full and shortened forms:

But other terms and phrases use lower case when spelled out in full, even though their acronym or initialism takes capitals:

Some acronyms have become so well established that they do not take full capitals, and do not need to be defined or included in a list of shortened forms:

If a sentence opens with a shortened form that starts with a lower-case letter (e.g. a technical term such as mRNA), rewrite the sentence so that the shortened form does not appear at the beginning of the sentence, or write the term in full:

For brand names that usually start with a lower-case letter (e.g. eBay, iPhone), capitalise the first letter if the word occurs at the beginning of a sentence or rewrite the sentence so that the shortened form does not appear at the beginning:

Articles with acronyms and initialisms

In running text, you will often need to use articles (a, an or the) before an acronym or initialism.

a/an

When a or an is required before an acronym, use the one that sounds correct when reading the text aloud. This means going by the sound at the start of the word, rather than whether it is written as a vowel or consonant:

the

In general, use the with initialisms, but not with acronyms:

Use the article the before initialisms used as nouns, but not when they are used as modifiers before a noun:

Some house styles tend not to use the with initialisms for government departments, but do use it for government agencies:

Very well known acronyms and initialisms

Acronyms and initialisms that are more familiar to your readership than the full title or phrase need not be written out in full on first mention. However, they should be included in the publication’s list of shortened forms (see Lists of shortened forms).

Familiar acronyms and initialisms may include:

Alternatively, for familiar acronyms or initialisms, you can reverse the order by using the shortened form before the full term:

Think about your readership when deciding whether to spell out terms. The following examples would be well known to particular readerships, and may not need to be spelled out if you know your audience will understand them:

Terms associated with established digital technologies do not need to be spelled out in full in the body of the publication or included in the list of shortened forms:

Organisation names that have changed over time

The official names of some organisations now consist of just the shortened form. The original name that was the basis for the shortened form is never used; it should not be included in the text or in the list of shortened forms:

The shortened form for some other organisation names no longer fully reflects the original name, or reflects the organisation’s name in another language; these should be spelled out at first use, as usual:

Always check each organisation’s preferred official name and shortened form on their website or in their publications.