Trondheimsfjorden is an inlet of the Norwegian Sea, is Norway's third-longest fjord at 130 km (81 mi) long. It is located in the west-central part of the country, and it stretches from Ørland in the west to Steinkjer in the north, passing the city of Trondheim on its way. Its maximum depth is 617 metres (2,024 ft), just inside of Agdenes.

The largest islands in the fjord are Ytterøy and Tautra; the small island of Munkholmen is located near the harbor of Trondheim; and there are several islands at the entrance of the fjord. The narrow Skarnsundet is crossed by the Skarnsund Bridge. The part of the fjord to the north of the strait is referred to as Beitstadfjorden. The main part of Trondheim Fjord is ice-free all year; only Verrasundet, a long and narrow fjord branch in the northern part of the fjord, might be ice covered in winter. The Beitstadfjorden might also freeze over in winter, but only for a few weeks.