Ayin (also ayn or ain; transliterated ⟨ʿ⟩) is the sixteenth letter of the Semitic scripts, including Phoenician ʿayin , Hebrew ʿayin ע‎, Aramaic ʿē , Syriac ʿē ܥ, and Arabic ʿayn ع (where it is sixteenth in abjadi order only).

The letter represents a voiced pharyngeal fricative (/ʕ/) or a similarly articulated consonant. In some Semitic languages and dialects, the phonetic value of the letter has changed, or the phoneme has been lost altogether (thus, in the revived Modern Hebrew it is reduced to a glottal stop or is omitted entirely in part due to European influence).

The Phoenician letter is the origin of the Greek, Latin and Cyrillic letter O, O and O.

It is the origin of letter Ƹ.