|Letter a with diacritic acute|
A diacritic (also diacritical mark, diacritical point, diacritical sign, or accent) is a glyph added to a letter or basic glyph. The term derives from the Ancient Greek διακριτικός (diakritikós, "distinguishing"), from διακρίνω (diakrī́nō, "to distinguish"). Diacritic is primarily an adjective, though sometimes used as a noun, whereas diacritical is only ever an adjective. Some diacritical marks, such as the acute ( ´ ) and grave ( ` ), are often called accents. Diacritical marks may appear above or below a letter, or in some other position such as within the letter or between two letters.
The main use of diacritical marks in the Latin script is to change the sound-values of the letters to which they are added. Examples are the diaereses in the borrowed French words naïve and Noël, which show that the vowel with the diaeresis mark is pronounced separately from the preceding vowel; the acute and grave accents, which can indicate that a final vowel is to be pronounced, as in saké and poetic breathèd; and the cedilla under the "c" in the borrowed French word façade, which shows it is pronounced / s/ rather than / k/. In other Latin-script alphabets, they may distinguish between homonyms, such as the French là ("there") versus la ("the") that are both pronounced /la/. In Gaelic type, a dot over a consonant indicates lenition of the consonant in question.
In other alphabetic systems, diacritical marks may perform other functions. Vowel pointing systems, namely the Arabic harakat ( ـِ ,ـُ ,ـَ, etc.) and the Hebrew niqqud ( ַ◌, ֶ◌, ִ◌, ֹ◌, ֻ◌, etc.) systems, indicate vowels that are not conveyed by the basic alphabet. The Indic virama ( ् etc.) and the Arabic sukūn ( ـْـ ) mark the absence of vowels. Cantillation marks indicate prosody. Other uses include the Early Cyrillic titlo stroke ( ◌҃ ) and the Hebrew gershayim ( ״ ), which, respectively, mark abbreviations or acronyms, and Greek diacritical marks, which showed that letters of the alphabet were being used as numerals. In the Hanyu Pinyin official romanization system for Chinese, diacritics are used to mark the tones of the syllables in which the marked vowels occur.
In orthography and collation, a letter modified by a diacritic may be treated either as a new, distinct letter or as a letter–diacritic combination. This varies from language to language, and may vary from case to case within a language. English is the only major modern European language requiring no diacritics for native words (although a diaeresis may be used in words such as "coöperation").  
In some cases, letters are used as "in-line diacritics", with the same function as ancillary glyphs, in that they modify the sound of the letter preceding them, as in the case of the "h" in the English pronunciation of "sh" and "th". 
Among the types of diacritic used in alphabets based on the Latin script are:
- accents (so called because the acute, grave, and circumflex were originally used to indicate different types of pitch accents in the polytonic transcription of Greek)
- vertical stroke
- macron or horizontal line
- ◌̊ – overring
- superscript curls
- subscript curls
- double marks (over or under two base characters)
- double sub/superscript diacritics
The tilde, dot, comma, titlo, apostrophe, bar, and colon are sometimes diacritical marks, but also have other uses.
Not all diacritics occur adjacent to the letter they modify. In the Wali language of Ghana, for example, an apostrophe indicates a change of vowel quality, but occurs at the beginning of the word, as in the dialects ’Bulengee and ’Dolimi. Because of vowel harmony, all vowels in a word are affected, so the scope of the diacritic is the entire word. In abugida scripts, like those used to write Hindi and Thai, diacritics indicate vowels, and may occur above, below, before, after, or around the consonant letter they modify.
The tittle (dot) on the letter i or the letter j, of the Latin alphabet originated as a diacritic to clearly distinguish i from the minims (downstrokes) of adjacent letters. It first appeared in the 11th century in the sequence ii (as in ingeníí), then spread to i adjacent to m, n, u, and finally to all lowercase is. The j, originally a variant of i, inherited the tittle. The shape of the diacritic developed from initially resembling today's acute accent to a long flourish by the 15th century. With the advent of Roman type it was reduced to the round dot we have today. 
Languages from Eastern Europe tend to use diacritics on both consonants and vowels, whereas in Western Europe digraphs are more typically used to change consonant sounds. Most languages in Western Europe use diacritics on vowels, aside from English where there are typically none (with some exceptions).
- (ئ ؤ إ أ and stand alone ء) hamza: indicates a glottal stop.
- (ــًــٍــٌـ) tanwīn (تنوين) symbols: Serve a grammatical role in Arabic. The sign ـً is most commonly written in combination with alif, e.g. ـًا.
- (ــّـ) shadda: Gemination (doubling) of consonants.
- (ٱ) waṣla: Comes most commonly at the beginning of a word. Indicates a type of hamza that is pronounced only when the letter is read at the beginning of the talk.
- (آ) madda: A written replacement for a hamza that is followed by an alif, i.e. (ءا). Read as a glottal stop followed by a long /aː/, e.g. ءاداب، ءاية، قرءان، مرءاة are written out respectively as آداب، آية، قرآن، مرآة. This writing rule does not apply when the alif that follows a hamza is not a part of the stem of the word, e.g. نتوءات is not written out as نتوآت as the stem نتوء does not have an alif that follows its hamza.
- (ــٰـ) superscript alif (also "short" or "dagger alif": A replacement for an original alif that is dropped in the writing out of some rare words, e.g. لاكن is not written out with the original alif found in the word pronunciation, instead it is written out as لٰكن.
- ḥarakāt (In Arabic: حركات also called تشكيل tashkīl):
- (ــَـ) fatḥa (a)
- (ــِـ) kasra (i)
- (ــُـ) ḍamma (u)
- (ــْـ) sukūn (no vowel)
- The ḥarakāt or vowel points serve two purposes:
- They serve as a phonetic guide. They indicate the presence of short vowels (fatḥa, kasra, or ḍamma) or their absence (sukūn).
- At the last letter of a word, the vowel point reflects the
inflection case or conjugation mood.
- For nouns, The ḍamma is for the nominative, fatḥa for the accusative, and kasra for the genitive.
- For verbs, the ḍamma is for the imperfective, fatḥa for the perfective, and the sukūn is for verbs in the imperative or jussive moods.
- Vowel points or tashkīl should not be confused with consonant points or iʿjam (إعجام) – one, two or three dots written above or below a consonant to distinguish between letters of the same or similar form.
These diacritics are used in addition to the acute, grave, and circumflex accents and the diaeresis:
- ◌ͺ (ᾳ, εͅ, ῃ, ιͅ, οͅ, υͅ, ῳ) – iota subscript
- ῾◌ – rough breathing ( Ancient Greek: δασὺ πνεῦμα, romanized: dasỳ pneûma, Latin: spīritus asper): aspiration
- ᾿◌ – smooth (or soft) breathing ( Ancient Greek: ψιλὸν πνεῦμα, romanized: psilòn pneûma, Latin: spīritus lēnis): lack of aspiration
- Cantillation marks do not generally render correctly; refer to Cantillation#Names and shapes of the ta'amim for a complete table together with instructions for how to maximize the possibility of viewing them in a web browser
The diacritics >〮 and 〯 , known as Bangjeom (방점; 傍點), were used to mark pitch accents in Hangul for Middle Korean. They were written to the left of a syllable in vertical writing and above a syllable in horizontal writing.
The South Korean government officially revised the romanization of the Korean language in July 2000 to eliminate diacritics.
- A dot above and a dot below a letter represent [a], transliterated as a or ă,
- Two diagonally-placed dots above a letter represent [ɑ], transliterated as ā or â or å,
- Two horizontally-placed dots below a letter represent [ɛ], transliterated as e or ĕ; often pronounced [ɪ] and transliterated as i in the East Syriac dialect,
- Two diagonally-placed dots below a letter represent [e], transliterated as ē,
- A dot underneath the Beth represent a soft [v] sound, transliterated as v
- A tilde (~) placed under Gamel represent a [dʒ] sound, transliterated as j
- The letter Waw with a dot below it represents [u], transliterated as ū or u,
- The letter Waw with a dot above it represents [o], transliterated as ō or o,
- The letter Yōḏ with a dot beneath it represents [i], transliterated as ī or i,
- A tilde (~) under Kaph represent a [t͡ʃ] sound, transliterated as ch or č,
- A semicircle under Peh represents an [f] sound, transliterated as f or ph.
In addition to the above vowel marks, transliteration of Syriac sometimes includes ə, e̊ or superscript e (or often nothing at all) to represent an original Aramaic schwa that became lost later on at some point in the development of Syriac.  Some transliteration schemes find its inclusion necessary for showing spirantization or for historical reasons.  
Some non-alphabetic scripts also employ symbols that function essentially as diacritics.
- Non-pure abjads (such as Hebrew and Arabic script) and abugidas use diacritics for denoting vowels. Hebrew and Arabic also indicate consonant doubling and change with diacritics; Hebrew and Devanagari use them for foreign sounds. Devanagari and related abugidas also use a diacritical mark called a virama to mark the absence of a vowel. In addition, Devanagari uses the moon-dot chandrabindu ( ँ ).
- Unified Canadian Aboriginal Syllabics use several types of diacritics, including the diacritics with alphabetic properties known as Medials and Finals. Although long vowels originally were indicated with a negative line through the Syllabic glyphs, making the glyph appear broken, in the modern forms, a dot above is used to indicate vowel length. In some of the styles, a ring above indicates a long vowel with a [j] off-glide. Another diacritic, the "inner ring" is placed at the glyph's head to modify [p] to [f] and [t] to [θ]. Medials such as the "w-dot" placed next to the Syllabics glyph indicates a [w] being placed between the syllable onset consonant and the nucleus vowel. Finals indicate the syllable coda consonant; some of the syllable coda consonants in word medial positions, such as with the "h-tick", indicate the fortification of the consonant in the syllable following it.
- The Japanese hiragana and katakana syllabaries use the dakuten (◌゛) and handakuten (◌゜) (in Japanese: 濁点 and 半濁点) symbols, also known as nigori (濁 "muddying") or ten-ten (点々 "dot dot") and maru (丸 "circle"), to indicate voiced consonants or other phonetic changes.
- Emoticons are commonly created with diacritic symbols, especially Japanese emoticons on popular imageboards.
Different languages use different rules to put diacritic characters in alphabetical order. French and Portuguese treat letters with diacritical marks the same as the underlying letter for purposes of ordering and dictionaries.
The Scandinavian languages and the Finnish language, by contrast, treat the characters with diacritics å, ä, and ö as distinct letters of the alphabet, and sort them after z. Usually ä (a-umlaut) and ö (o-umlaut) [used in Swedish and Finnish] are sorted as equivalent to æ (ash) and ø (o-slash) [used in Danish and Norwegian]. Also, aa, when used as an alternative spelling to å, is sorted as such. Other letters modified by diacritics are treated as variants of the underlying letter, with the exception that ü is frequently sorted as y.
Languages that treat accented letters as variants of the underlying letter usually alphabetize words with such symbols immediately after similar unmarked words. For instance, in German where two words differ only by an umlaut, the word without it is sorted first in German dictionaries (e.g. schon and then schön, or fallen and then fällen). However, when names are concerned (e.g. in phone books or in author catalogues in libraries), umlauts are often treated as combinations of the vowel with a suffixed e; Austrian phone books now treat characters with umlauts as separate letters (immediately following the underlying vowel).
In Spanish, the grapheme ñ is considered a new letter different from n and collated between n and o, as it denotes a different sound from that of a plain n. But the accented vowels á, é, í, ó, ú are not separated from the unaccented vowels a, e, i, o, u, as the acute accent in Spanish only modifies stress within the word or denotes a distinction between homonyms, and does not modify the sound of a letter.
For a comprehensive list of the collating orders in various languages, see Collating sequence.
Modern computer technology was developed mostly in English-speaking countries, so data formats, keyboard layouts, etc. were developed with a bias favoring English, a language with an alphabet without diacritical marks. Efforts have been made to create internationalized domain names that further extend the English alphabet (e.g., "pokémon.com").
Depending on the keyboard layout, which differs amongst countries, it is more or less easy to enter letters with diacritics on computers and typewriters. Some have their own keys; some are created by first pressing the key with the diacritic mark followed by the letter to place it on. Such a key is sometimes referred to as a dead key, as it produces no output of its own but modifies the output of the key pressed after it.
In modern Microsoft Windows and Linux operating systems, the keyboard layouts US International and UK International feature dead keys that allow one to type Latin letters with the acute, grave, circumflex, diaeresis, tilde, and cedilla found in Western European languages (specifically, those combinations found in the ISO Latin-1 character set) directly: ¨ + e gives ë, ~ + o gives õ, etc. On Apple Macintosh computers, there are keyboard shortcuts for the most common diacritics; Option-e followed by a vowel places an acute accent, Option-u followed by a vowel gives an umlaut, Option-c gives a cedilla, etc. Diacritics can be composed in most X Window System keyboard layouts, as well as other operating systems, such as Microsoft Windows, using additional software.
On computers, the availability of code pages determines whether one can use certain diacritics. Unicode solves this problem by assigning every known character its own code; if this code is known, most modern computer systems provide a method to input it. With Unicode, it is also possible to combine diacritical marks with most characters. However, as of 2019, very few fonts include the necessary support to correctly render character-plus-diacritic(s) for the Latin, Cyrillic and some other alphabets (exceptions include Andika).
The following languages have letters that contain diacritics that are considered independent letters distinct from those without diacritics.
- Latvian has the following letters: ā, ē, ī, ū, č, ģ, ķ, ļ, ņ, š, ž
- Lithuanian. In general usage, where letters appear with the caron (č, š and ž), they are considered as separate letters from c, s or z and collated separately; letters with the ogonek ( ą, ę, į and ų), the macron ( ū) and the superdot ( ė) are considered as separate letters as well, but not given a unique collation order.
- Welsh uses the circumflex, diaeresis, acute, and grave on its seven vowels a, e, i, o, u, w, y (hence the composites â, ê, î, ô, û, ŵ, ŷ, ä, ë, ï, ö, ü, ẅ, ÿ, á, é, í, ó, ú, ẃ, ý, à, è, ì, ò, ù, ẁ, ỳ).
- Following spelling reforms since the 1970s, Scottish Gaelic uses graves only, which can be used on any vowel ( à, è, ì, ò, ù). Formerly acute accents could be used on á, ó and é, which were used to indicate a specific vowel quality. With the elimination of these accents, the new orthography relies on the reader having prior knowledge of pronunciation of a given word.
- Manx uses the single diacritic ç combined with h to give the digraph ⟨çh⟩ (pronounced /tʃ/) to mark the distinction between it and the digraph ⟨ch⟩ (pronounced /h/ or /x/). Other diacritics used in Manx included â, ê, ï, etc. to mark the distinction between two similarly spelled words but with slightly differing pronunciation.
- Irish uses only acute accents to mark long vowels, following the 1948 spelling reform.
- Breton does not have a single orthography (spelling system), but uses diacritics for a number of purposes. The diaeresis is used to mark that two vowels are pronounced separately and not as a diphthong/digraph. The circumflex is used to mark long vowels, but usually only when the vowel length is not predictable by phonology. Nasalization of vowels may be marked with a tilde, or following the vowel with the letter <ñ>. The plural suffix -où is used as a unified spelling to represent a suffix with a number of pronunciations in different dialects, and to distinguish this suffix from the digraph <ou> which is pronounced as /u:/. An apostrophe is used to distinguish c'h, pronounced /x/ as the digraph <ch> is used in other Celtic languages, from the French-influenced digraph ch, pronounced /ʃ/.
- Cyrillic alphabets
- Belarusian and Uzbek Cyrillic have a letter ў.
- Belarusian, Bulgarian, Russian and Ukrainian have the letter й.
- Belarusian and Russian have the letter ё. In Russian, this letter is usually replaced by е, although it has a different pronunciation. The use of е instead of ё does not affect the pronunciation. Ё is always used in children's books and in dictionaries. A minimal pair is все (vs'e, "everybody" pl.) and всё (vs'o, "everything" n. sg.). In Belarusian the replacement by е is a mistake; in Russian, it is permissible to use either е or ё for ё but the former is more common in everyday writing (as opposed to instructional or juvenile writing).
- The Cyrillic Ukrainian alphabet has the letters ґ, й and ї. Ukrainian Latynka has many more.
- Macedonian has the letters ќ and ѓ.
- In Bulgarian and Macedonian the possessive pronoun ѝ (ì, "her") is spelled with a grave accent in order to distinguish it from the conjunction и (i, "and").
- The acute accent " ́" above any vowel in Cyrillic alphabets is used in dictionaries, books for children and foreign learners to indicate the word stress, it also can be used for disambiguation of similarly spelled words with different lexical stresses.
- Estonian has a distinct letter õ, which contains a tilde. Estonian "dotted vowels" ä, ö, ü are similar to German, but these are also distinct letters, not like German umlauted letters. All four have their own place in the alphabet, between w and x. Carons in š or ž appear only in foreign proper names and loanwords. Also these are distinct letters, placed in the alphabet between s and t.
- Finnish uses dotted (umlauted) vowels (ä and ö). As in Swedish and Estonian, these are regarded as individual letters, rather than vowel + umlaut combinations (as happens in German). It also uses the characters å, š and ž in foreign names and loanwords. In the Finnish and Swedish alphabets, å, ä and ö collate as separate letters after z, the others as variants of their base letter.
- Hungarian uses the umlaut, the acute and double acute accent (unique to Hungarian): (ö, ü), (á, é, í, ó, ú) and (ő, ű). The acute accent indicates the long form of a vowel (in case of i/í, o/ó, u/ú) while the double acute performs the same function for ö and ü. The acute accent can also indicate a different sound (more open, like in case of a/á, e/é). Both long and short forms of the vowels are listed separately in the Hungarian alphabet, but members of the pairs a/á, e/é, i/í, o/ó, ö/ ő, u/ú and ü/ ű are collated in dictionaries as the same letter.
- Livonian has the following letters: ā, ä, ǟ, ḑ, ē, ī, ļ, ņ, ō, ȯ, ȱ, õ, ȭ, ŗ, š, ț, ū, ž.
- Faroese uses acutes and other special letters. All are considered separate letters and have their own place in the alphabet: á, í, ó, ú, ý and ø.
- Icelandic uses acutes and other special letters. All are considered separate letters, and have their own place in the alphabet: á, é, í, ó, ú, ý, and ö.
- Danish and Norwegian use additional characters like the o-slash ø and the a-overring å. These letters come after z and æ in the order ø, å. Historically, the å has developed from a ligature by writing a small superscript a over a lowercase a; if an å character is unavailable, some Scandinavian languages allow the substitution of a doubled a. The Scandinavian languages collate these letters after z, but have different collation standards.
- Swedish uses a-diaeresis ( ä) and o-diaeresis ( ö) in the place of ash (æ) and slashed o ( ø) in addition to the a-overring (å). Historically, the diaeresis for the Swedish letters ä and ö, like the German umlaut, developed from a small Gothic e written above the letters. These letters are collated after z, in the order å, ä, ö.
- In Asturian, Galician and Spanish, the character ñ is a letter and collated between n and o.
- Asturian uses Ḷ ( lower case ḷ), and Ḥ ( lower case ḥ) 
- Leonese: could use ñ or nn.
- Romanian uses a breve on the letter a ( ă) to indicate the sound schwa /ə/, as well as a circumflex over the letters a ( â) and i ( î) for the sound /ɨ/. Romanian also writes a comma below the letters s ( ș) and t ( ț) to represent the sounds /ʃ/ and /t͡s/, respectively. These characters are collated after their non-diacritic equivalent.
- The Bosnian, Croatian, and Serbian Latin alphabets have the symbols č, ć, đ, š and ž, which are considered separate letters and are listed as such in dictionaries and other contexts in which words are listed according to alphabetical order. They also have one digraph including a diacritic, dž, which is also alphabetized independently, and follows d and precedes đ in the alphabetical order. The Serbian Cyrillic alphabet has no diacritics, instead it has a grapheme ( glyph) for every letter of its Latin counterpart (including Latin letters with diacritics and the digraphs dž, lj and nj).
- The Czech alphabet uses the acute (á é í ó ú ý), caron ( č ď ě ň ř š ť ž), and for one letter ( ů) the ring. (Note that in ď and ť the caron is modified to look lither[ clarification needed] like an apostrophe.)
- Polish has the following letters: ą ć ę ł ń ó ś ź ż. These are considered to be separate letters: each of them is placed in the alphabet immediately after its Latin counterpart (e.g. ą between a and b), ź and ż are placed after z in that order.
- The Slovak alphabet uses the acute (á é í ó ú ý ĺ ŕ), caron (č ď ľ ň š ť ž), umlaut (ä) and circumflex accent (ô). 
- The basic Slovenian alphabet has the symbols č, š, and ž, which are considered separate letters and are listed as such in dictionaries and other contexts in which words are listed according to alphabetical order. Letters with a caron are placed right after the letters as written without the diacritic. The letter đ may be used in non-transliterated foreign words, particularly names, and is placed after č and before d.
- Azerbaijani includes the distinct Turkish alphabet letters Ç, Ğ, I, İ, Ö, Ş and Ü.
- Crimean Tatar includes the distinct Turkish alphabet letters Ç, Ğ, I, İ, Ö, Ş and Ü. Unlike Standard Turkish (but like Cypriot Turkish), Crimean Tatar also has the letter Ñ.
- Gagauz includes the distinct Turkish alphabet letters Ç, Ğ, I, İ, Ö and Ü. Unlike Turkish, Gagauz also has the letters Ä, Ê Ș and Ț. Ș and Ț are derived from the Romanian alphabet for the same sounds. Sometime the Turkish Ş may be used instead of Ș.
- Turkish uses a G with a breve ( Ğ), two letters with an umlaut ( Ö and Ü, representing two rounded front vowels), two letters with a cedilla ( Ç and Ş, representing the affricate /tʃ/ and the fricative /ʃ/), and also possesses a dotted capital İ (and a dotless lowercase ı representing a high unrounded back vowel). In Turkish each of these are separate letters, rather than versions of other letters, where dotted capital İ and lower case i are the same letter, as are dotless capital I and lowercase ı. Typographically, Ç and Ş are sometimes rendered with a subdot, as in Ṣ; when a hook is used, it tends to have more a comma shape than the usual cedilla[ citation needed]. The new Azerbaijani, Crimean Tatar, and Gagauz alphabets are based on the Turkish alphabet and its same diacriticized letters, with some additions.
- Turkmen includes the distinct Turkish alphabet letters Ç, Ö, Ş and Ü. In addition, Turkmen uses A with diaeresis ( Ä) to represent /æ/, N with caron ( Ň) to represent the velar nasal /ŋ/, Y with acute ( Ý) to represent the palatal approximant /j/, and Z with caron ( Ž) to represent /ʒ/.
- Albanian has two special letters Ç and Ë upper and lowercase. They are placed next to the most similar letters in the alphabet, c and e correspondingly.
- Esperanto has the symbols ŭ, ĉ, ĝ, ĥ, ĵ and ŝ, which are included in the alphabet, and considered separate letters.
- Filipino also has the character ñ as a letter and is collated between n and o.
- Hawaiian uses the kahakō ( macron) over vowels, although there is some disagreement over considering them as individual letters. The kahakō over a vowel can completely change the meaning of a word that is spelled the same but without the kahakō.
- Kurdish uses the symbols Ç, Ê, Î, Ş and Û with other 26 standard Latin alphabet symbols.
- Lakota alphabet uses the caron for the letters č, ȟ, ǧ, š, and ž. It also uses the acute accent for stressed vowels á, é, í, ó, ú, áŋ, íŋ, úŋ.
- Malay uses some diacritics such as â, ā, ç, î, ñ, ô, š, û. Uses of diacritics was continued until late 19th century except ā and ē.
- Maltese uses a C, G, and Z with a dot over them (Ċ, Ġ, Ż), and also has an H with an extra horizontal bar. For uppercase H, the extra bar is written slightly above the usual bar. For lowercase H, the extra bar is written crossing the vertical, like a t, and not touching the lower part ( Ħ, ħ). The above characters are considered separate letters. The letter 'c' without a dot has fallen out of use due to redundancy. 'Ċ' is pronounced like the English 'ch' and 'k' is used as a hard c as in 'cat'. 'Ż' is pronounced just like the English 'Z' as in 'Zebra', while 'Z' is used to make the sound of 'ts' in English (like 'tsunami' or 'maths'). 'Ġ' is used as a soft 'G' like in 'geometry', while the 'G' sounds like a hard 'G' like in 'log'. The digraph 'għ' (called għajn after the Arabic letter name ʻayn for غ) is considered separate, and sometimes ordered after 'g', whilst in other volumes it is placed between 'n' and 'o' (the Latin letter 'o' originally evolved from the shape of Phoenician ʻayin, which was traditionally collated after Phoenician nūn).
- The romanization of Syriac uses the altered letters of. Ā, Č, Ḏ, Ē, Ë, Ġ, Ḥ, Ō, Š, Ṣ, Ṭ, Ū, Ž alongside the 26 standard Latin alphabet symbols. 
- Vietnamese uses the horn diacritic for the letters ơ and ư; the circumflex for the letters â, ê, and ô; the breve for the letter ă; and a bar through the letter đ.
English is one of the few European languages that does not have many words that contain diacritical marks. Instead, digraphs are the main way the Modern English alphabet adapts the Latin to its phonemes. Exceptions are unassimilated foreign loanwords, including borrowings from French and, increasingly, Spanish like jalapeño; however, the diacritic is also sometimes omitted from such words. Loanwords that frequently appear with the diacritic in English include café, résumé or resumé (a usage that helps distinguish it from the verb resume), soufflé, and naïveté (see English terms with diacritical marks). In older practice (and even among some orthographically conservative modern writers) one may see examples such as élite, mêlée and rôle.
English speakers and writers once used the diaeresis more often than now in words such as coöperation (from Fr. coopération), zoölogy (from Grk. zoologia), and seeër (now more commonly see-er or simply seer) as a way of indicating that adjacent vowels belonged to separate syllables, but this practice has become far less common. The New Yorker magazine is a major publication that continues to use the diaeresis in place of a hyphen for clarity and economy of space. 
A few English words, out of context, can only be distinguished from others by a diacritic or modified letter, including exposé, lamé, maté, öre, øre, pâté, and rosé'. The same is true of résumé, alternately resumé, but nevertheless it is regularly spelled resume. In a few words, diacritics that did not exist in the original have been added for disambiguation, as in maté (from Sp. and Port. mate), saké (the standard Romanization of the Japanese has no accent mark), and Malé (from Dhivehi މާލެ), to clearly distinguish them from the English words "mate", "sake", and "male".
The acute and grave accents are occasionally used in poetry and lyrics: the acute to indicate stress overtly where it might be ambiguous (rébel vs. rebél) or nonstandard for metrical reasons (caléndar), the grave to indicate that an ordinarily silent or elided syllable is pronounced (warnèd, parlìament).
In certain personal names such as Renée and Zoë, often two spellings exist, and the preference will be known only to those close to the person themselves. Even when the name of a person is spelled with a diacritic, like Charlotte Brontë, this may be dropped in English language articles and even official documents such as passports either due to carelessness, the typist not knowing how to enter letters with diacritical marks, or for technical reasons— California, for example, does not allow names with diacritics, as the computer system cannot process such characters. They also appear in some worldwide company names and/or trademarks such as Nestlé or Citroën.
The following languages have letter-diacritic combinations that are not considered independent letters.
- Afrikaans uses a diaeresis to mark vowels that are pronounced separately and not as one would expect where they occur together, for example voel (to feel) as opposed to voël (bird). The circumflex is used in ê, î, ô and û generally to indicate long close-mid, as opposed to open-mid vowels, for example in the words wêreld (world) and môre (morning, tomorrow). The acute accent is used to add emphasis in the same way as underlining or writing in bold or italics in English, for example Dit is jóú boek (It is your book). The grave accent is used to distinguish between words that are different only in placement of the stress, for example appel (apple) and appèl (appeal) and in a few cases where it makes no difference to the pronunciation but distinguishes between homophones. The two most usual cases of the latter are in the sayings òf... òf (either... or) and nòg... nòg (neither... nor) to distinguish them from of (or) and nog (again, still).
- Aymara uses a diacritical horn over p, q, t, k, ch.
- Catalan has the following composite characters: à, ç, é, è, í, ï, ó, ò, ú, ü, l·l. The acute and the grave indicate stress and vowel height, the cedilla marks the result of a historical palatalization, the diaeresis indicates either a hiatus, or that the letter u is pronounced when the graphemes gü, qü are followed by e or i, the interpunct (·) distinguishes the different values of ll/l·l.
- Some orthographies of Cornish such as Kernowek Standard and Unified Cornish use diacritics, while others such as Kernewek Kemmyn and the Standard Written Form do not (or only use them optionally in teaching materials).
- Dutch uses the diaeresis. For example, in ruïne it means that the u and the i are separately pronounced in their usual way, and not in the way that the combination ui is normally pronounced. Thus it works as a separation sign and not as an indication for an alternative version of the i. Diacritics can be used for emphasis (érg koud for very cold) or for disambiguation between a number of words that are spelled the same when context doesn't indicate the correct meaning (één appel = one apple, een appel = an apple; vóórkomen = to occur, voorkómen = to prevent). Grave and acute accents are used on a very small number of words, mostly loanwords. The ç also appears in some loanwords. 
- Faroese. Non-Faroese accented letters are not added to the Faroese alphabet. These include é, ö, ü, å and recently also letters like š, ł, and ć.
- Filipino has the following composite characters: á, à, â, é, è, ê, í, ì, î, ó, ò, ô, ú, ù, û. The actual use of diacritics for Filipino is, however, uncommon, meant only to distinguish between homonyms with different stresses and meanings that either occur near each other in a text or to aid the reader in ascertaining its otherwise ambiguous meaning. The letter eñe is due to the Spanish alphabet and too, is considered a separate letter. The diacritics appears in Spanish loanwords and names if Spanish orthography is observed.
- Finnish. Carons in š and ž appear only in foreign proper names and loanwords, but may be substituted with sh or zh if and only if it is technically impossible to produce accented letters in the medium. Contrary to Estonian, š and ž are not considered distinct letters in Finnish.
- French uses five diacritics. The grave (accent grave) marks the sound /ɛ/ when over an e, as in père ("father") or is used to distinguish words that are otherwise homographs such as a/à ("has"/"to") or ou/où ("or"/"where"). The acute (accent aigu) is only used in "é", modifying the "e" to make the sound /e/, as in étoile ("star"). The circumflex (accent circonflexe) generally denotes that an S once followed the vowel in Old French or Latin, as in fête ("party"), the Old French being feste and the Latin being festum. Whether the circumflex modifies the vowel's pronunciation depends on the dialect and the vowel. The cedilla (cédille) indicates that a normally hard "c" (before the vowels "a", "o", and "u") is to be pronounced /s/, as in ça ("that"). The diaeresis (tréma) indicates that two adjacent vowels that would normally be pronounced as one are to be pronounced separately, as in Noël ("Christmas").
- Galician vowels can bear an acute (á, é, í, ó, ú) to indicate stress or difference between two otherwise same written words (é, 'is' vs. e, 'and'), but the diaeresis (trema) is only used with ï and ü to show two separate vowel sounds in pronunciation. Only in foreign words may Galician use other diacritics such as ç (common during the Middle Ages), ê, or à.
- German uses the three umlauted characters ä, ö and ü. These diacritics indicate vowel changes. For instance, the word Ofen [ˈoːfən] "oven" has the plural Öfen [ˈøːfən]. The mark originated as a superscript e; a handwritten blackletter e resembles two parallel vertical lines, like a diaeresis. Due to this history, "ä", "ö" and "ü" can be written as "ae", "oe" and "ue" respectively, if the umlaut letters are not available.
- Hebrew has many various diacritic marks known as niqqud that are used above and below script to represent vowels. These must be distinguished from cantillation, which are keys to pronunciation and syntax.
- The International Phonetic Alphabet uses diacritic symbols and characters to indicate phonetic features or secondary articulations.
- Irish uses the acute to indicate that a vowel is long: á, é, í, ó, ú. It is known as síneadh fada "long sign" or simply fada "long" in Irish. In the older Gaelic type, overdots are used to indicate lenition of a consonant: ḃ, ċ, ḋ, ḟ, ġ, ṁ, ṗ, ṡ, ṫ.
- Italian mainly has the acute and the grave (à, è/é, ì, ò/ó, ù), typically to indicate a stressed syllable that would not be stressed under the normal rules of pronunciation but sometimes also to distinguish between words that are otherwise spelled the same way (e.g. "e", and; "è", is). Despite its rare use, Italian orthography allows the circumflex (î) too, in two cases: it can be found in old literary context (roughly up to 19th century) to signal a syncope (fêro→fecero, they did), or in modern Italian to signal the contraction of ″-ii″ due to the plural ending -i whereas the root ends with another -i; e.g., s. demonio, p. demonii→demonî; in this case the circumflex also signals that the word intended is not demoni, plural of "demone" by shifting the accent (demònî, "devils"; dèmoni, "demons").
- Lithuanian uses the acute, grave and tilde in dictionaries to indicate stress types in the language's pitch accent system.
- Maltese also uses the grave on its vowels to indicate stress at the end of a word with two syllables or more:– lowercase letters: à, è, ì, ò, ù ; capital letters: À, È, Ì, Ò, Ù
- Māori makes use of macrons to mark long vowels.
- Occitan has the following composite characters: á, à, ç, é, è, í, ï, ó, ò, ú, ü, n·h, s·h. The acute and the grave indicate stress and vowel height, the cedilla marks the result of a historical palatalization, the diaeresis indicates either a hiatus, or that the letter u is pronounced when the graphemes gü, qü are followed by e or i, and the interpunct (·) distinguishes the different values of nh/n·h and sh/s·h (i.e., that the letters are supposed to be pronounced separately, not combined into "ny" and "sh").
- Portuguese has the following composite characters: à, á, â, ã, ç, é, ê, í, ó, ô, õ, ú. The acute and the circumflex indicate stress and vowel height, the grave indicates crasis, the tilde represents nasalization, and the cedilla marks the result of a historical lenition.
- Acutes are also used in Slavic language dictionaries and textbooks to indicate lexical stress, placed over the vowel of the stressed syllable. This can also serve to disambiguate meaning (e.g., in Russian писа́ть (pisáť) means "to write", but пи́сать (písať) means "to piss"), or "бо́льшая часть" (the biggest part) vs "больша́я часть" (the big part).
- Spanish uses the acute and the diaeresis. The acute is used on a vowel in a stressed syllable in words with irregular stress patterns. It can also be used to "break up" a diphthong as in tío (pronounced [ˈti.o], rather than [ˈtjo] as it would be without the accent). Moreover, the acute can be used to distinguish words that otherwise are spelled alike, such as si ("if") and sí ("yes"), and also to distinguish interrogative and exclamatory pronouns from homophones with a different grammatical function, such as donde/¿dónde? ("where"/"where?") or como/¿cómo? ("as"/"how?"). The acute may also be used to avoid typographical ambiguity, as in 1 ó 2 ("1 or 2"; without the acute this might be interpreted as "1 0 2". The diaeresis is used only over u (ü) for it to be pronounced [w] in the combinations gue and gui, where u is normally silent, for example ambigüedad. In poetry, the diaeresis may be used on i and u as a way to force a hiatus. As foreshadowed above, in nasal ñ the tilde (squiggle) is not considered a diacritic sign at all, but a composite part of a distinct glyph, with its own chapter in the dictionary: a glyph that denotes the 15th letter of the Spanish alphabet.
- Swedish uses the acute to show non-standard stress, for example in kafé (café) and resumé (résumé). This occasionally helps resolve ambiguities, such as ide (hibernation) versus idé (idea). In these words, the acute is not optional. Some proper names use non-standard diacritics, such as Carolina Klüft and Staël von Holstein. For foreign loanwords the original accents are strongly recommended, unless the word has been infused into the language, in which case they are optional. Hence crème fraîche but ampere. Swedish also has the letters å, ä, and ö, but these are considered distinct letters, not a and o with diacritics.
- Tamil does not have any diacritics in itself, but uses the Arabic numerals 2, 3 and 4 as diacritics to represent aspirated, voiced, and voiced-aspirated consonants when Tamil script is used to write long passages in Sanskrit.
- Thai has its own system of diacritics derived from Indian numerals, which denote different tones.
- Vietnamese uses the acute (dấu sắc), the grave (dấu huyền), the tilde (dấu ngã), the underdot (dấu nặng) and the hoi (dấu hỏi) on vowels as tone indicators.
- Welsh uses the circumflex, diaeresis, acute, and grave on its seven vowels a, e, i, o, u, w, y. The most common is the circumflex (which it calls to bach, meaning "little roof", or acen grom "crooked accent", or hirnod "long sign") to denote a long vowel, usually to disambiguate it from a similar word with a short vowel. The rarer grave accent has the opposite effect, shortening vowel sounds that would usually be pronounced long. The acute accent and diaeresis are also occasionally used, to denote stress and vowel separation respectively. The w-circumflex and the y-circumflex are among the most commonly accented characters in Welsh, but unusual in languages generally, and were until recently very hard to obtain in word-processed and HTML documents.
Several languages that are not written with the Roman alphabet are transliterated, or romanized, using diacritics. Examples:
- Arabic has several romanisations, depending on the type of the application, region, intended audience, country, etc. many of them extensively use diacritics, e.g., some methods use an underdot for rendering emphatic consonants (ṣ, ṭ, ḍ, ẓ, ḥ). The macron is often used to render long vowels. š is often used for /ʃ/, ġ for /ɣ/.
- Chinese has several romanizations that use the umlaut, but only on u (ü). In Hanyu Pinyin, the four tones of Mandarin Chinese are denoted by the macron (first tone), acute (second tone), caron (third tone) and grave (fourth tone) diacritics. Example: ā, á, ǎ, à.
- Romanized Japanese ( Rōmaji) occasionally uses macrons to mark long vowels. The Hepburn romanization system uses macrons to mark long vowels, and the Kunrei-shiki and Nihon-shiki systems use a circumflex.
- Sanskrit, as well as many of its descendants, like Hindi and Bengali, uses a lossless romanization system. This includes several letters with diacritical markings, such as the macron (ā, ī, ū), over- and underdots (ṛ, ḥ, ṃ, ṇ, ṣ, ṭ, ḍ) as well as a few others (ś, ñ).
Possibly the greatest number of combining diacritics required to compose a valid character in any Unicode language is 8, for the "well-known grapheme cluster in Tibetan and Ranjana scripts",ཧྐྵྨླྺྼྻྂ, or HAKṢHMALAWARAYAṀ. 
It is U+0F67 U+0F90 U+0FB5 U+0FA8 U+0FB3 U+0FBA U+0FBC U+0FBB U+0F82, or:
TIBETAN LETTER HA + TIBETAN SUBJOINED LETTER KA + TIBETAN SUBJOINED LETTER SSA + TIBETAN SUBJOINED LETTER MA + TIBETAN SUBJOINED LETTER LA + TIBETAN SUBJOINED LETTER FIXED-FORM WA + TIBETAN SUBJOINED LETTER FIXED-FORM RA + TIBETAN SUBJOINED LETTER FIXED-FORM YA + TIBETAN SIGN NYI ZLA NAA DA.
Some users have explored the limits of rendering in web browsers and other software by "decorating" words with multiple nonsensical diacritics per character. The result is called " Zalgo text". The composed bogus characters and words can be copied and pasted normally via the system clipboard.
- Latin-script alphabets
- Alt code
- Category:Letters with diacritics
- Collating sequence
- Combining character
- Compose key
- English terms with diacritical marks
- Heavy metal umlaut
- ISO/IEC 8859 8-bit extended-Latin-alphabet European character encodings
- Latin alphabet
- List of Latin letters
- List of precomposed Latin characters in Unicode
- List of U.S. cities with diacritics
- wikt:Appendix:English words with diacritics
- As an example, an article containing a diaeresis in "coöperate" and a cedilla in "façades" as well as a circumflex in the word "crêpe" (Grafton, Anthony (2006-10-23). "Books: The Nutty Professors, The history of academic charisma". The New Yorker.)
- "The New Yorker's odd mark — the diaeresis". 16 December 2010. Archived from the original on 16 December 2010.
- Henry Sweet (1877) A Handbook of Phonetics, p 174–175: "Even letters with accents and diacritics [...] being only cast for a few founts, act practically as new letters. [...] We may consider the h in sh and th simply as a diacritic written for convenience on a line with the letter it modifies."
- Oxford English Dictionary
- Nestle, Eberhard (1888). Syrische Grammatik mit Litteratur, Chrestomathie und Glossar. Berlin: H. Reuther's Verlagsbuchhandlung. [translated to English as Syriac grammar with bibliography, chrestomathy and glossary, by R. S. Kennedy. London: Williams & Norgate 1889].
- Coakley, J. F. (2002). Robinson's Paradigms and Exercises in Syriac Grammar (5th ed.). Oxford University Press. ISBN 978-0-19-926129-1.
- Michaelis, Ioannis Davidis (1784). Grammatica Syriaca.
- Gramática de la Llingua Asturiana (PDF) (3rd ed.). Academia de la Llingua Asturiana. 2001. section 1.2. ISBN 84-8168-310-8. Archived from the original (PDF) on 2011-05-25. Retrieved 2011-06-07.
- http://www.juls.savba.sk/ediela/psp2000/psp.pdf page 12, section I.2
- S.P. Brock, "An Introduction to Syriac Studies", in J.H. Eaton (Ed.,), Horizons in Semitic Studies (1980)
- Norris, Mary. "The Curse of the Diaeresis". The New Yorker. Retrieved 18 April 2014.
- van Geloven, Sander (2012). Diakritische tekens in het Nederlands (in Dutch). Utrecht: Hellebaard. Archived from the original on 2013-10-29.
- Steele, Shawn (2010-01-25). "Most combining characters in a Unicode glyph/character/whatever". Microsoft. Archived from the original on 2019-05-16. Retrieved 2019-11-25.