A diacritic (diacritique en français ; diacrítico em português'') is a mark placed in proximity to a character (like letter of an alphabet) that adds some value to the pronunciation (sound of the letter or tone of the vowel) or to the meaning. In the Latin script (Roman alphabet) these include accent marks, indicators of tone, and marks such as subdots that change the pronunciation of a particular letter. In the Arabic script, vowel markings may be considered as diacritic marks. In N'Ko, diacritics that indicate tone are an integral part of the writing system.

In Unicode, there are some character + diacritic combinations in Latin ranges that are precomposed characters?, such as many letters with accents used in European languages and many subdot letters (the latter in the Latin Extended Additional? range. Unicode also provides for diacritics on other characters in Latin by use of combining diacritics? which may be added above or below a base character? using dynamic composition?.