Ellesmere Island, a large island in the Arctic Ocean off northwestern Greenland. It is part of Nunavut, a Canadian territory. The island is about 500 miles (800 km) long and up to 300 miles (480 km) wide; it has an area of 75,767 square miles (196,236 km2). The surface is mountainous and mostly ice-covered. The highest peak, in the north, rises to about 8,500 feet (2,600 m). Part of the island is occupied by Ellesmere Island National Park.

Ellesmere was discovered by the English navigator William Baffin in 1616.