PSO may refer to:
In music:
- Peoria Symphony Orchestra
- Pittsburgh Symphony Orchestra
- Portland Symphony Orchestra
In science and technology:
- Particle swarm optimization, a swarm intelligence optimization technique
- Phase-shift oscillator, an electronic circuit that generates sine waves
- Protocol Support Organization, one of the three initial components of ICANN, later disbanded
- Password Settings Object, used in Windows Active Directory environments
- Project Support Officer
Other uses:
- Pakistan State Oil
- Paysite operator, the operator of a paysite, typically pornographic
- Penalty shootout, a method of determining a winner in sports matches which would have otherwise been drawn or tied
- Phantasy Star Online, a video game
- Phone sex operator, a person who provides phone sex service
- PSO-1, A Soviet telescopic sight
- Producers Sales Organization, an independent motion picture production and distribution company
- Public service obligation, a form of state subsidy for transport links which are not commercially viable
- Puro Sangue Orientale, a breed of horse in Italy