FSO

• Federal Protective Service (Russia) (Russian: {{lang|ru-Latn|Federalnaya Sluzhba Okhrany}}), responsible for the security of Russian state officials
• Federal Statistical Office (Switzerland)
• Financial Secretary's Office, of the Government of Hong Kong
• Foreign Service Officer, of the United States Foreign Service
• Forest Section Officer, in India

• Fairfax Symphony Orchestra, in Virginia, United States
• Frankston Symphony Orchestra, in Victoria, Australia
• Fulham Symphony Orchestra, in London
• "F.S.O.", the first single from the Regurgitator album Tu-Plang
• Film Symphony Orchestra, Czech classical orchestra

• Fabryka Samochodów Osobowych, a Polish automotive company
• Franklin County State Airport, in Vermont, United States
• Subiaco railway station, in Western Australia

• Fire Support Officer
• Flash shared object
• Floating storage and offloading
• Free-space optical communication
• Flag Service Organization

{{disambiguation}}