Tröllaskagi is a peninsula in northern Iceland on the Greenland Sea, between the fjords of Eyjafjörður and Skagafjörður. The peninsula is mountainous, with several peaks reaching over 1,000 meters above sea level, the tallest being Kerling (1,538 m). It is the part of Iceland with the highest elevation outside the central highlands.

The peninsula is cut by several deep valleys that were carved by glaciers during the glacial periods of the last Ice age and later by the rivers that now flow down those valleys. A few permanent glacial ice caps still exist in central Tröllaskagi, but they are all rather small.