PSO may refer to:

In music:

• Pacific Symphony Orchestra
• Peoria Symphony Orchestra
• Pittsburgh Symphony Orchestra
• Plano Symphony Orchestra
• Portland Symphony Orchestra
• Perth Symphony Orchestra (Western Australia)

In science and technology:

• Particle swarm optimization, a swarm intelligence optimization technique
• Password Settings Object, used in Windows Active Directory environments
• Phase-shift oscillator, an electronic circuit that generates sine waves
• Protocol Support Organization, one of the three initial components of ICANN, later disbanded
• PSO J318.5-22, a rogue planet discovered in 2013

Other uses:

• Pakistan State Oil
• Patient safety organization
• Paysite operator, the operator of a paysite, typically pornographic
• Peace Support Operations, a military term used by NATO
• Penalty shootout, a method of determining a winner in sports matches which would have otherwise been drawn or tied
• Phantasy Star Online, a series of online role-playing video games
  • Phantasy Star Online, the first game in the series
• Phone sex operator, a person who provides phone sex service
• Producers Sales Organization, an independent motion picture production and distribution company
• Protective services officer, a member of police in Australia who performs policing duties at specific locations
• Psoriasis, an autoimmune disease
• PSO-1, a Soviet telescopic sight
• Public Safety Officer, another name for police, firefighters, ambulance crews and other providing safety services in the U.S.
• Public Service Company of Oklahoma
• 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
• The FAA LID code for Stevens Field airport in Archuleta County, Colorado, United States.
• The IATA code for Antonio Nariño Airport, serving the Colombian city of Pasto
• It also refers to Personal Security Officers.
• Provider Services Operations, a team at the National Marrow Donor Program