Gaf (Persian: گاف; gāf), is the name of different Perso-Arabic letters, all representing /ɡ/. They are all derived from the letter kāf, with additional diacritics, such as dots and lines. In name and shape, it is a variant of kaf. It is also one of the five letters the Persian alphabet added to the Arabic alphabet (the others being ژ, پ, and چ in addition to the obsolete ڤ). Its numerical value is 5000 (see Abjad numerals). There are four forms, each used in different alphabets:

A non-standard letter to the Arabic alphabet; Gāf (گ) has been traditionally used in Iraq and parts of the Levant for /g/. In Morocco, a similar letter (ݣ‎) is used. while in other Arabic-speaking countries other letters are used, such as ڨ‎ in Tunisia and Algeria, and any of the standard letters ج‎, غ‎, or ق‎ in the other countries.

The most common form of gāf (گ‎) is based on kāf with an additional line. It is rarely used in Standard Arabic itself but is used to represent the sound /ɡ/ when writing other languages.

When representing this sound in transliteration of Persian into Hebrew, it is written as כ׳ kaph and a geresh.

It is frequently used in Persian, Pashto, Uyghur, Urdu and Kurdish, and is one of four Perso-Arabic letters not found in Arabic. It is also commonly used in Mesopotamian Arabic.

In Pashto, this letter is used for /ɡ/.

This gāf (ݢ‎) is derived from a variant form of kāf (ک‎), with the addition of a dot. It is not used in the Arabic language itself, but is used in the Jawi script to represent /ɡ/.

Unicode includes two forms on this letter: one based on the standard Arabic kāf (ك‎), and one based on the variant form (ک‎). The latter is the preferred form.