Trondheim, historically Kaupangen, Nidaros and Trondhjem, is a city and municipality in Trøndelag county, Norway. As of 2022, it had a population of 212,660. Trondheim is the third most populous municipality in Norway, and was the fourth largest urban area. Trondheim lies on the south shore of Trondheim Fjord at the mouth of the River Nidelva. Among the significant technology-oriented institutions headquartered in Trondheim are the Norwegian University of Science and Technology (NTNU), the Foundation for Scientific and Industrial Research (SINTEF), the Geological Survey of Norway (NGU), and St. Olavs University Hospital.

The Trondheim Fjord or Trondheimsfjorden, an inlet of the Norwegian Sea, is Norway's third-longest fjord at 130 kilometres (81 mi) long. It is located in the west-central part of the country in Trøndelag county, and it stretches from the municipality of Ørland in the west to the municipality of Steinkjer in the north, passing the city of Trondheim on its way. Its maximum depth is 617 metres (2,024 ft), between Orkland and Indre Fosen.