FSN may refer to:
- Fate/stay night, a visual novel and its adaptations.
- The Federal Stock Number, a numeric code used to identify items in the Joint Army-Navy Catalog System.
- The Federation of Student Nationalists: the student wing of the Scottish National Party.
- Filter Smoke Number
- Five-seveN, a semi-automatic pistol designed and manufactured by FN Herstal in Belgium.
- Forest Star Networks, a Telecom Operator Enabler within the VoIP and Fixed & Mobile VNO and Metro Networks segment.
- Fox Sports Networks, a national network of regional sports channels in the United States
- Fox Sports News, an Australian cable and satellite sports news channel.
- Full Service Network, a Pittsburgh based competitive local exchange carrier
- Full Service Network, a defunct digital video broadcasting service
- FSN Broadband, an Internet and Broadband Phone Service Provider
- Global Forum on Food Security and Nutrition
- Fronte Sociale Nazionale (National Social Front), an Italian far right political party
- Frontul Salvării Naţionale (National Salvation Front), a former revolutionary group and governing political party of Romania
- Fsn, a 3-D file manager that appeared in the movie Jurassic Park