Ø (or minuscule: ø) is a vowel and a letter used in the Danish, Norwegian, Faroese, and Southern Sami languages. It is mostly used as a representation of mid front rounded vowels, such as [ø] and [œ], except for Southern Sami where it is used as an [oe] diphthong.

The name of this letter is the same as the sound it represents (see usage). Though not its native name, among English-speaking typographers the symbol may be called a "slashed O"[1] or "o with stroke". Although these names suggest it is a ligature or a diacritical variant of the letter o, it is considered a separate letter in Norwegian and Danish, and it is alphabetized after "z"—thus z, æ, ø, and å.

In other languages that do not have the letter as part of the regular alphabet, or in limited character sets such as ASCII, ø may correctly be replaced with the digraph "oe", although in practice it is often replaced with just an "o", e.g. in email addresses. It is equivalent to the letter ö used in Swedish (and a number of other languages), and may also be replaced with ö, as was often the case with older typewriters in Denmark and Norway.

ø (lower case) is also used in the International Phonetic Alphabet to represent a close-mid front rounded vowel.