PS or ps may stand for:
- postscript (most commonly), a portion of a letter labelled P.S. added after the main body of the letter was written. It stands for post scriptum, a Latin expression meaning "after writing".
- Parti socialiste or Partido Socialista (Socialist Party)
- Pferdestärke -- German for horsepower
- Political science
- polystyrene, the resin identification code
- PostScript, page description language for computers
- Proton Synchrotron
- Public school in the United States, often as part of the number of an unnamed school, such as P.S. 31.