Trondheim, historically Kaupangen, Nidaros and Trondhjem, is a city and municipality in Trøndelag county, Norway. It has a population of 205,332 as of 2020, and is the third most populous municipality in Norway, although the fourth largest urban area. Trondheim lies on the south shore of Trondheim Fjord at the mouth of the River Nidelva. Among the major technology-oriented institutions headquartered in Trondheim are the Norwegian University of Science and Technology, the Foundation for Scientific and Industrial Research, and St. Olavs University Hospital.
The settlement was founded in 997 as a trading post, and it served as the capital of Norway during the Viking Age until 1217. From 1152 to 1537, the city was the seat of the Catholic Archdiocese of Nidaros; since then, it has remained the seat of the Lutheran Diocese of Nidaros and the Nidaros Cathedral. It was incorporated in 1838. The current municipality dates from 1964, when Trondheim merged with Byneset, Leinstrand, Strinda and Tiller.
Trondheim has a very mild climate for its northerly latitude, resulting in moderate summers and winters that often remain above the freezing point in seaside areas.