Fenrir, Fenrisulfr, or Fenris is a Norse mythological wolf. It may also refer to:
- Fenrir (moon), a moon of Saturn named after Fenrisulfr
- Fenris, designation of a battlemech in the science-fiction series BattleTech
- Fenrir, a monster card in the Yu-Gi-Oh! Trading Card Game
- Fenris, homeworld of the Space Wolves Space Marine chapter in the Warhammer 40,000 universe
- Fenrir Inc, Japanese developer of the Sleipnir web browser
- Fenris Glacier, a glacier in eastern Greenland