In many languages, the letter "ö", or the "o" modified with an umlaut, is used to denote the close- or open-mid front rounded vowels [ø] ⓘ or [œ] ⓘ.

In Danish and Norwegian, ö was previously used in place of ø in older texts to distinguish between open and closed ö-sounds.

In other languages that do not have the letter as part of the regular alphabet or in limited character sets such as ASCII, o-umlaut is frequently replaced with the digraph oe.

Its name in Finnish, Swedish, Icelandic, Estonian, Azeri, Turkish, Turkmen, Uyghur, Crimean Tatar, Hungarian, Votic and Volapük is Öö [øː], not "O with two dots" since /ø/ is not a variant of the vowel /o/ but a distinct phoneme.

In some alphabets it is collated as an independent letter, sometimes by placing it at or near the end of the alphabet, such as after Z, Å and Ä in Swedish and Finnish, after Ý, (Z), Þ and Æ in Icelandic, and after V, (W), Õ and Ä in Estonian (thus fulfilling the place of omega, for example in the Finnish expression aasta ööhön "from A to Z", literally "from A to Ö".

In these languages the letter represents the fact that this o is the start of a new syllable (e.g. in the Dutch/Afrikaans word coöperatief [cooperative]), instead of the general oo (e.g.

In the Rheinische Dokumenta, a phonetic alphabet for many West Central German, the Low Rhenish, and few related vernacular languages, ö represents the close-mid front rounded vowel with the IPA notation [ø].

The origin of the letter ö was a similar ligature for the digraph OE: e was written above o and degenerated into two small dots.

[citation needed] In some inscriptions and display typefaces, ö may be represented as an o with a small letter e inside.

In modern typography there was insufficient space on typewriters and later computer keyboards to allow for both an O-with-dots (also representing ö) and an o-with-bars[clarification needed].