Ï

Ï, lowercase ï, is a symbol used in various languages written with the Latin alphabet; it can be read as the letter I with diaeresis, I-umlaut or I-trema.

Initially in French and also in Afrikaans, Catalan, Dutch, Galician, Southern Sami, Welsh, and occasionally English, $\langleï\rangle$ is used when $\langlei\rangle$ follows another vowel and indicates hiatus in the pronunciation of such a word. It indicates that the two vowels are pronounced in separate syllables, rather than together as a diphthong or digraph. For example, French maïs (, maize); without the diaeresis, the $\langlei\rangle$ is part of the digraph $\langleai\rangle$: mais (, but). The letter is also used in the same context in Dutch, as in Oekraïne (, Ukraine), and English naïve ( or  ).

In scholarly writing on Turkic languages, $⟨ï⟩$ is sometimes used to write the close back unrounded vowel, which, in the standard modern Turkish alphabet, is written as the dotless i $⟨ı⟩$. The back neutral vowel reconstructed in Proto-Mongolic is sometimes written $⟨ï⟩$.

In the transcription of Amazonian languages, ï is used to represent the high central vowel.

It is also a transliteration of the rune ᛇ.

Computing
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). Thus, it tends to indicate that any following mojibake can be corrected by reinterpreting the data as UTF-8.