FSK can have alternative meanings:
- Federal Counterintelligence Service, (Federalnaya Sluzhba Kontrrazvedki, Федера́льная Слу́жба Контрразве́дки), Federal Counterintelligence Service of Russia)
- Frequency-shift keying, an electronic communications modulation scheme
- Forsvarets Spesialkommando (FSK), a Norwegian special forces military unit
- FSK (band), a German band
- Freiwillige Selbstkontrolle der Filmwirtschaft, a German movie rating organization
- Fsk, pen name for Boštjan Čadež, creator of Line Rider