YY

YY may refer to:

* Yo-yo
* Yakety Yak: The Coasters doo-wop song
* Yakkity Yak: A Nicktoons Network show.
* XYY syndrome: A generic aneuploidy in which the Y chromosome is duplicated.
* Peptide YY 3-36: A peptide that is secreted by the gut in response to a meal, and reduces appetite.