YY

YY or variants may refer to:


 * YY.com, a major Chinese social network
 * yy (digraph), digraph used in various Latin alphabets
 * Yy (musician), Canadian musician
 * YY, the call sign prefix for radio stations in Venezuela
 * Y. Y., pseudonym of Robert Wilson Lynd (1879–1949), Irish essayist
 * Peptide YY 3-36, a peptide secreted by the gut in response to a meal, and reduces appetite
 * YY, the production code for the 1969 Doctor Who serial The Space Pirates