FSF may refer to:

• Free Software Foundation, an American non-profit organization with a mission to promote computer user freedom
• Federal Security Force (Pakistan)
• Federación de Sindicatos Ferroviarios, a defunct Argentine trade union
• Financial Stability Forum, a defunct international organization of financial regulators
• Flight Safety Foundation, an international independent, non-profit organization for research, education, and communications in the field of civil aviation flight safety
• Föreningen Sveriges Filmfotografer, the Swedish Society of Cinematographers
• Progressive Party, an Icelandic political party (in Icelandic: Framsóknarflokkurinn)
• Freiwillige Selbstkontrolle Fernsehen, German television rating content board.

• Folsom Street Fair, a street fair in San Francisco, California, United States
• Further Seems Forever, a rock band
• Fugitive Strike Force, a 2006 television series
• The Magazine of Fantasy & Science Fiction, also abbreviated F&SF
• Speculative fiction (genre) containing the subgenre of fantasy/science fiction (F/SF)
• Science fantasy (genre), a mixed genre of fantasy and science fiction elements
• Festival of Slovenian Film, an annual film festival in Portorož, Slovenia

• Faroe Islands Football Association (Faroese: Fótbóltssamband Føroya)
• Federação Sergipana de Futebol, the Football Federation of Sergipe, Brazil
• Football Supporters' Federation
• Fuerte San Francisco, a Salvadoran football club
• Sahrawi Football Federation (Spanish: Federación Saharaui de Fútbol)
• São Toméan Football Federation (Portuguese: Federação Santomense de Futebol)
• Senegalese Footrrball Federation (French: Fédération Sénégalaise de Football)

• Familial Shar Pei fever
• Fibrin-stabilizing factor
• Flexible Support Fund in the United Kingdom
• Fourth suit forcing, a bidding convention in the game of contract bridge
• Free speech fights, a series of 20th-century labor-related conflicts in the United States
• Full state feedback