Thusis (Italian: Tosana, Romansh: Tusàn) is a municipality in the Viamala Region in the Swiss canton of the Grisons . On 1 January 2018 the former municipality of Mutten merged into the municipality of Thusis.

Thusis is first mentioned in 1156 as Tosana. The town was devastated by more than 10 fires and after the one of 1845, it had to be rebuilt.

Thusis has an area, as of 2006, of 6.8 km2 (2.6 sq mi). Of this area, 18% is used for agricultural purposes, while 58.2% is forested.