Indre Fosen is a municipality in Trøndelag county, Norway. It is located in the traditional district of Fosen. The administrative centre of the municipality is the village of Årnset. Other villages in Indre Fosen include Askjem, Dalbygda, Hasselvika, Husbysjøen, Leira, Leksvik, Råkvåg, Rørvika, Seter, Stadsbygd, Sørfjorden, Verrabotn, and Vanvikan. The Norwegian County Road 755 runs through the municipality.

The 1,096-square-kilometre (423 sq mi) municipality is the 102nd largest by area out of the 357 municipalities in Norway. Indre Fosen Municipality is the 113th most populous municipality in Norway with a population of 10,023. The municipality's population density is 9.1 inhabitants per square kilometre (24/sq mi) and its population has decreased by 1.7% over the previous 10-year period.

Economy: in January 2024, a shipyard that employed 132, went bankrupt.

The municipality was established on 1 January 2018, the same day that Trøndelag county was established. Indre Fosen Municipality straddles the former county border, as it was formed by the unification of Leksvik Municipality (formerly in Nord-Trøndelag) and Rissa Municipality (formerly in Sør-Trøndelag).

On 1 January 2020, the Verrabotn area from the neighboring Verran Municipality was transferred to Indre Fosen Municipality.

The municipality is named after the traditional district of Fosen in which it is located. The first element is indre which means "inner" in the Norwegian language. The last element is Fosen (Old Norse: Fólgsn) which means "hiding place" or "hidden port". Thus, the name refers to the inner part of the Fosen district. The district is named after the island of Storfosna ("Big Fosen") in Ørland Municipality.

The coat of arms was adopted in 2017 for use starting on 1 January 2018 when the new municipality was established. These arms were originally granted to the old Leksvik Municipality on 28 September 1990 and then they were re-adopted for the new Indre Fosen Municipality after the merger of Leksvik Municipality and Rissa Municipality. The official blazon is "Per chevron embowed azure and argent point ending in trefoil" (Norwegian: I blått en innbøyd sølv spiss som ender i et kløverblad). This means the arms have a field (background) that is divided by a line in the shape of a chevron with curved sides that meet at a point. A trefoil is located on top of this point. The background above the line is blue and the background below this line has a tincture of argent which means it is commonly colored white, but if it is made out of metal, then silver is used. The blue part represents the Trondheimsfjord and the white/silver part represents the land, particularly the Amborneset peninsula where King Sverre Sigurdsson fought his last sea battle on 8 June 1198. There is a clover/trefoil design at the end of the silver part which represents life and growth. The arms were designed by Einar H. Skjærvold.

The Church of Norway has six parishes (Norwegian: sogn, which is both singular and plural) within the municipality. Together with the other municipalities on the Fosen peninsula (Osen, Ørland, and Åfjord), Indre Fosen is part of the Fosen prosti (deanery) in the Diocese of Nidaros.