Yn is an archaic Cyrillic letter. It looks like the Cyrillic letter Psi turned upside down.
It was used in the Romanian Cyrillic alphabet, where it represented the sounds , , and at the beginning of words. In the modern Romanian alphabet it is replaced by , , or .
YN, Y.N., or Yn may refer to:
- Yn , a letter of the old Romanian Cyrillic alphabet
- yn, a word in the Welsh language for "in"
- Yeoman rank
- Triple bond in a chemical compound
- Y.N. Hosakote, a village in the southern state of Karnataka, India
- 2C-YN, an analogue of the phenethylamine derived hallucinogen 2C-E where the ethyl group has been replaced by an ethynyl group.
- Yn question, an abbreviation for Yes-no question