The article concerns the origin and development of the Slavic vowel *y in Slavic languages. At the starting point I present the articulatory characteristics of contemporary Polish y, and then move on to the late Indo-European vocal system - the primordial source of the discussed sound. Then I move on to the analysis of the circumstances of the creation of the phoneme y including phonetics - delabialisation *ū1, and phonology - change *ū1 → y as a consequence of the creation of ū2 from the monophthongisation of diphthongs. I also present the views of researchers on the old pronunciation of y. In the main part of the article I focus on the analysis of the occurrence and functioning of y in various Slavic languages, including dialects, without losing sight of the accompanying historical perspective.