Ammassalik Island is an island in the Sermersooq municipality in southeastern Greenland, with an area of 772 km2 . The island is separated from the mainland of Greenland by the wide Sermilik Fjord in the west, and by the Ikaasartivaq Strait in the northeast.
In the east and southeast the southern, progressively wider half of the Ammassalik Fjord separates the island from an archipelago of islands, including the largest Apusiaajik Island, and Kulusuk Island across the Torsuut Tunoq sound. The southern coast of the island is washed by the waters of the open North Atlantic.
The highest point of the island is a glaciated peak in the northern part, at 1,352 m (4,435.7 ft. The only settlement on the island is Tasiilaq town, with 1,893 inhabitants as of 2009, the most populous community on the eastern coast, and the seventh-largest town in Greenland.