Yu (Ю, ю) is a letter of the Cyrillic alphabet, representing either the combination (a so-called iotated vowel) or after a palatalized consonant.

Apart from the form I-O, in early Slavonic manuscripts the letter appears also in a mirrored form O-I. It is this form that is probably original, precisely displaying the Greek combination omicron-iota (οι). At the time the Greek alphabet was adapted to the Slavonic language (giving rise to the Cyrillic alphabet), this was pronounced as a Close front rounded vowel | in educated Greek speech. This digraphic representation of was so basic for speakers of Greek that the simple letter upsilon (υ) representing the same sound came to be called υ ψιλόν (y psilon) 'simple y' in contrast to 'complex' οι.

Probably in analogy to the 'iotated' letters , ІА, and , which fulfilled similar functions in Slavonic, this OI ligature was soon mirrored to the modern form Ю.

Vowel letters

Ю (lizherenn) | Ю (Cirillico) | Ю | Ю (кириллица) | Ю | Ю