Soon after the code words were developed by ICAO (see history below), they were adopted by other national and international organizations, including the ITU, the International Maritime Organization (IMO), the United States Federal Government as Federal Standard 1037C: Glossary of Telecommunications Terms and its successors ANSI T1.523-2001 and ATIS Telecom Glossary (ATIS-0100523.2019) (all three using the spellings "Alpha" and "Juliet"), the United States Department of Defense, the Federal Aviation Administration (FAA) (using the spelling "Xray"), the International Amateur Radio Union (IARU), the American Radio Relay League (ARRL), the Association of Public-Safety Communications Officials-International (APCO), and by many military organizations such as NATO (using the spelling "Xray") and the now-defunct Southeast Asia Treaty Organization (SEATO).

The same alphabetic code words are used by all agencies, but each agency chooses one of two different sets of numeric code words. NATO uses the regular English numerals (zero, one, two, etc., though with some differences in pronunciation), whereas the ITU (beginning on 1 April 1969) and the IMO created compound code words (nadazero, unaone, bissotwo etc.). In practice the compound words are used very rarely.

A spelling alphabet is used to distinguish those parts of a message that contain letters and digits, because the names of many letters sound similar, for instance bee and pee, en and em or ef and ess. The potential for confusion increases if static or other interference is present, as is commonly the case with radio and telephonic communication. For instance, the target message "proceed to map grid DH98" would be transmitted as proceed to map grid Delta-Hotel-Niner-Ait.

Civilian industry uses the code words to avoid similar problems in the transmission of messages by telephone systems. For example, it is often used in the retail industry where customer or site details are conveyed by telephone (for example to authorize a credit agreement or confirm stock codes), although ad-hoc code words are often used in that instance. It has been used by information technology workers to communicate serial numbers and reference codes, which are often very long, by voice. Most major airlines use the alphabet to communicate passenger name records (PNRs) internally, and in some cases, with customers. It is often used in a medical context as well.

Several codes words and sequences of code words have become well-known, such as Bravo Zulu (letter code BZ) for "well done", Checkpoint Charlie (Checkpoint C) in Berlin, and Zulu Time for Greenwich Mean Time or Coordinated Universal Time. During the Vietnam War, the US government referred to the Viet Cong guerrillas and the group itself as VC, or Victor Charlie; the name "Charlie" became synonymous with this force.

The final choice of code words for the letters of the alphabet and for the digits was made after hundreds of thousands of comprehension tests involving 31 nationalities. The qualifying feature was the likelihood of a code word being understood in the context of others. For example, Football has a higher chance of being understood than Foxtrot in isolation, but Foxtrot is superior in extended communication.

Pronunciations were set out by the ICAO before 1956 with advice from the governments of both the United States and United Kingdom. To eliminate national variations in pronunciation, posters illustrating the pronunciation desired by ICAO are available. However, there remain differences in the pronunciations published by ICAO and other agencies, and ICAO has apparently conflicting Latin-alphabet and IPA transcriptions. At least some of these differences appear to be typographic errors. In 2022 the Deutsches Institut für Normung (DIN) attempted to resolve these conflicts. For example, they consistently transcribe [a] for what the ICAO had transcribed variously as [a], [aː], [ɑ], [ɑː], [æ], [ə] in IPA and as a, ah, ar, er in orthography.

Just as words are spelled out as individual letters, numbers are spelled out as individual digits. That is, 17 is rendered as one seven and 60 as six zero. Depending on context, the word thousand may be used as in English, and for whole hundreds only (when the sequence 00 occurs at the end of a number), the word hundred may be used. For example, 1300 is read as one three zero zero if it is a transponder code or serial number, and as one thousand three hundred if it is an altitude or distance.

The ICAO, NATO, and FAA use modifications of English digits as code words, with 3, 4, 5 and 9 being pronounced tree, fower (rhymes with lower), fife and niner. The digit 3 is specified as tree so that it will not be mispronounced sri (and similarly for thousand); the long pronunciation of 4 (still found in some English dialects) keeps it somewhat distinct from for; 5 is pronounced with a second "f" because the normal pronunciation with a "v" is easily confused with "fire"; and 9 has an extra syllable to keep it distinct from the German word nein "no". (Prior to 1956, three and five had been pronounced with the English consonants, but with the vowels broken into two syllables.) For directions presented as the hour-hand position on a clock, the additional numerals "ten", "eleven" and "twelve" are used with the word "o'clock".

The ITU and IMO, however, specify a different set of code words. These are compounds of ICAO and Latinesque roots. The IMO's GMDSS procedures permits the use of either set of code words.
There are two IPA transcriptions of the letter names, from the International Civil Aviation Organization (ICAO) and the Deutsches Institut für Normung (DIN). Both authorities indicate that a non-rhotic pronunciation is standard. That of the ICAO, first published in 1950 and reprinted many times without correction (e.g. the error in 'golf'), uses a large number of vowels. For instance, it has six low/central vowels: [æ] [a] [aː] [ɑ] [ɑː] [ə]. The DIN consolidated all six into the single low-central vowel [a]. The DIN vowels are partly predictable, with [ɪ ɛ ɔ] in closed syllables and [i e/ei̯ o] in open syllables apart from echo and sierra, which have [ɛ] as in English, German and Italian. The DIN also reduced the number of stress…

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