Initially in French and also in Afrikaans, Catalan, Dutch, Galician, Southern Sami, Welsh, and occasionally English, ⟨ï⟩ is used when ⟨i⟩ follows another vowel and indicates hiatus in the pronunciation of such a word.

The letter is also used in the same context in Dutch, as in Oekraïne (pronounced [ukraːˈ(j)inə] ⓘ *and not [uˈkrɑinə]; "Ukraine"), and English naïve (/nɑːˈiːv/ nah-EEV or /naɪˈiːv/ ny-EEV).

In scholarly writing on Turkic languages, ⟨ï⟩ is sometimes used to write the close back unrounded vowel /ɯ/, which, in the standard modern Turkish alphabet, is written as the dotless i ⟨ı⟩.

[2] In the transcription of Amazonian languages, ⟨ï⟩ is used to represent the high central vowel [ɨ].

It is also a transliteration of the rune ᛇ. Lowercase ï is often seen in the sequences � and , which are the Unicode replacement character and byte order mark, respectively, in UTF-8 misinterpreted as ISO-8859-1 or CP1252 (both common encodings in software configured for English-language users).