FSO may stand for:
- Fabryka Samochodów Osobowych, a Polish car company
- Federal Protective Service of Russia responsible for the security of Russian state officials.
- Flash Shared Object a local shared cookie used in computing.
- Floating Storage and Offloading, system, is an offshore oil and gas vessel
- Foreign Service Officer, government employee working for their country in a foreign country
- Frank Skinner's Opinionated, British TV programme
- Free Space Optics, a wireless data transmission technology
- Forest Section Officer, an officer in the State Forest Services of the government of India
- Scripting.FileSystemObject in Windows Script Host
- Office of the Financial Secretary
- test and measurement sensor Full Scale Output
- Free-space optical communication, a technology that uses light to transmit data.