Trondheim is a city and municipality located in Trøndelag county, Norway. It sits on the south shore of Trondheim Fjord at the mouth of the Nidelva river. The settlement functions as the seat of the County Mayor of Trøndelag, although it does not serve as the administrative centre for the county. This arrangement is designed to prevent the centralization of county administration in Steinkjer.

The city was founded in 997 by Olav Tryggvason as a trading post named Kaupangen. It served as the capital of Norway through the Viking Age until 1217 and was the seat of the Catholic Archdiocese of Nidaros from 1152 to 1537. The name changed from Trondhjem to Trondheim in 1931, following a period where it was briefly called Drontheim during the Second World War.

The skyline is dominated by Nidaros Cathedral, the only Gothic cathedral in Norway and a site of royal coronations. The city centre lies within a large river bend, featuring broad avenues created after the 1681 Horneman Fire. Significant technology-oriented institutions headquartered here include the Norwegian University of Science and Technology, SINTEF, and the Geological Survey of Norway.

Trondheim is known for its student life, music, arts, and nightlife, attracting visitors with its historic religious heritage and technological profile. The city hosts Rosenborg football club and the Granåsen Ski Centre, which has held World Championships in Nordic skiing. Its history as a northern mercantile hub gives it an international culture distinct from other Scandinavian cities.

As of 1 January 2026, the municipality had a population of 218,460, making it the third most populous in Norway. The city has a mild oceanic climate for its northerly latitude, with moderate summers and winters that often remain above freezing in seaside areas due to the Gulf Stream. It is the fourth largest urban area in the country.