RSO or R.S.O. may refer to:
- Regional Security Officer, a U.S. Diplomatic Security Service (DSS) Special Agent in charge of security at a U.S. Embassy
- Regional Security Office, office from which Special Agents of the U.S. Diplomatic Security Service work - located at U.S. Embassies or Consulates overseas.
- Revised Statutes of Ontario, Canada
- Range Safety Officer, a person responsible for the safe use of rocket vehicles
- Radiation Safety Officer, a person responsible for the safe use of radiation and radioactive materials
- Raupenschlepper Ost, a fully tracked WW II German artillery tractor
- Reconnaissance Systems Officer, military personal in charge of optic equipment and radar-scrambling equipment in a spy plane
- Riverside Sheriff's Office, law enforcement provider for much of Riverside County, CA.
- Rogers Sportsnet Ontario, a television station in Ontario, Canada
- RSO Records, a record label formed by Robert Stigwood in the late 1960s
- Registered sex offender, a person that has been convicted of sexually abusing another person or animal
- Registered Sex Offender, a 2008 film released at SXSW directed by Bob Byington and starring Kristen Tucker and Gabriel McIver
- "Radio Symphony Orchestra", used by a number of orchestras:
- Danish National Symphony Orchestra, based in Copenhagen, Denmark
- North German Radio Symphony Orchestra, based in Hamburg, Germany
- Stuttgart Radio Symphony Orchestra, based in Stuttgart, Germany
- Bavarian Radio Symphony Orchestra, based in Munich, Germany
- Frankfurt Radio Symphony Orchestra, based in Frankfurt, Germany
- Finnish Radio Symphony Orchestra
- Swedish Radio Symphony Orchestra
- Vienna Radio Symphony Orchestra
- South Ossetia, Republic of South Ossetia
- Rohingya Solidarity Organization, a political organization of Burma (Myanmar) struggling for the basic human rights for the people of the Arakan State, especially Rohingya Muslims
- Reactive Search Optimization, problem-solving methods with integrated online machine-learning capabilities.