PS or ps may stand for:

• A picosecond, an SI unit of time equal to 10^-12 of a second.
• Pashto language (ISO 639 alpha-2, ps)
• 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, the French Socialist Party
• Parti Socialiste, a Belgian Socialist Party
• Partido Socialista, the Portuguese Socialist Party
• Pferdestärke -- German for horsepower
• PlayStation
• 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.
• power supply
• ps is an application distributed on Unix and Unix-like operating systems.
• P.S., a 2004 film
• Adobe Photoshop
• Priory of Sion
• The initials of Peter Salcher , physicist who pioneered ultrafast photography. His most famous work is that about shock waves, photographs of bullet etc.