Peptide YY is a short (36 amino acid) protein released by cells in the ileum and colon in response to feeding. It is also known as PYY, Peptide Tyrosine Tyrosine, or Pancreatic Peptide YY_3-36. Peptide YY is related to the pancreatic peptide family by having 18 of its 36 amino acids located in the same positions as pancreatic peptide. There are two major forms of Peptide YY: PYY_1-36 and PYY_3-36 which have PP fold structural motif.

However, the most common form of circulating PYY immunoreactivity is PYY_3-36 which binds to Y2 receptor (Y2R) of Y family receptors. Peptide YY_3-36 (PYY) is a linear polypeptide consisting of 36 amino acids with structural homology to NPY and pancreatic polypeptide.