Fosen is a traditional district in coastal Trøndelag county, Norway. The district consists of the municipalities Osen, Åfjord, Ørland, Indre Fosen, Orkland, Heim, Hitra, and Frøya.
In colloquial speech, Fosen also refers to the Fosen peninsula, (Indre Fosen, Åfjord, and Osen) with the peninsula also having the Southern Sami name Fovsa.