A circumfix or circumflection is an affix, a morpheme which is placed around another morpheme. Circumfixes contrast with prefixes, attached to the beginnings of words; suffixes, that are attached at the end; and infixes, inserted in the middle. See also epenthesis.

The circumfix is probably most widely known from the German past participle (ge- -t for regular verbs). The verb spielen, for example, has the participle gespielt.

For instance, in Hebrew magdelet "magnifier", the root is gdl "big" (in the H-stem hagdel "to enlarge") and the circumfix is m- -et. Similarly, in classical French, negation is achieved by the circumfix ne ... pas which is placed around either the chief verb or the auxiliary verb of a verb phrase. Circumfixes are extremely common in Bahasa Indonesia.

Probably the only circumfixes in English are: en- -en and em- -en in enlighten and embolden. One cannot say ^*enlight (although lighten is correct); ^*embold and ^*bolden are both incorrect. In older usage, however, the present participle could be formed using the circumfix a- -ing: Gather ye rosebuds while ye may,// Old time is still a-flying (Robert Herrick).