FO

Fo may refer to:

* Face Off
*Fo Fai, a character in the "Battle Arena Toshinden" video game series
* Abbreviation for the computer game Fallout (computer game)
* Faroe Islands (country code FO)
* Faroese language (language code fo)
* Field officer, a senior army officer
* First-order logic, a system of mathematical logic
* First Officer, or co-pilot on an airliner
* Flying Officer, a Royal Air Force rank
* Dario Fo, Italian playwright and Nobel laureate
* Football Outsiders, a website devoted to statistical analysis of the NFL
* "Force Ouvrière", a French trade unions confederation
* Foreign and Commonwealth Office of the British government
* Foreign object
* Foreign Objects, a Pennsylvania music group
* Forum, an online communications medium
* Forward Observer, a soldier who directs artillery fire
* Fourier number (Fo) in physics
* Frame optional military symbol
* Front Office
* Abbreviation for Fuck Off
* Fuel oil
* FunOrb, a Java-based gaming website
* Furka-Oberalp-Bahn, a Swiss railway
* Futures and Options
* Number 4 (slang abbreviation "fo’")
* XSL Formatting Objects (XSL-FO)
* Airlines of Tasmania IATA airline designator
* Fo, one of the 9 Departments of the Houet Province of Burkina Faso.
* FO, a subunit of F1FO type ATPase