Tinn is a municipality in Telemark county, Norway. It is part of the traditional region of Øst-Telemark. The administrative centre of the municipality is the town of Rjukan.
The parish of Tin was established as a municipality on 1 January 1838 (see formannskapsdistrikt). The area of Hovin was separated from the municipality of Tinn in 1860, but it was merged back into the municipality of Tinn on 1 January 1964.
Krossobanen is the oldest aerial tramway in Northern Europe. It was built in 1928 as a gift from Norsk Hydro. There is a museum and Hardangervidda National Park center at the lake Møsvatn close to Tinn.