在字体排印学中，组合字符（Combining character）是用来改变其它字符所用的字符。在拉丁文本中，最常见的组合字符为附加符号（包含重音号）。

统一码也包含许多预组字符（precomposed character），即事先将字符组好并赋予码位。所以有可能同时使用组合字符和预组字符。这导致了若要比较两个统一码字串或设计编码转换器时，需要先运行Unicode范式。

在统一码中，用于欧洲语言和国际音标的组合用附加符号为U+0300–U+036F。组合用附加符号亦存在统一码中的多个区块。在统一码中，附加符号总是加在主要字符之后。因此，有可能加入多个附加符号。直到2006年，只有少数软件能正确显示此类组合。

In digital typography, combining characters are characters that are intended to modify other characters. The most common combining characters in the Latin script are the combining diacritical marks (including combining accents).

Unicode also contains many precomposed characters, so that in many cases it is possible to use both combining diacritics and precomposed characters, at the user's or application's choice. This leads to a requirement to perform Unicode normalization before comparing two Unicode strings and to carefully design encoding converters to correctly map all of the valid ways to represent a character in Unicode to a legacy encoding to avoid data loss. In Unicode, the main block of combining diacritics for European languages and the International Phonetic Alphabet is U+0300–U+036F. Combining diacritical marks are also present in many other blocks of Unicode characters. In Unicode, diacritics are always added after the main character, so it is possible to add several diacritics to the same character, although as of 2010, few applications support correct rendering of such combinations.