Manus Island is part of Manus Province in northern Papua New Guinea and is the largest island of the Admiralty Islands. It is the fifth largest island in Papua New Guinea with an area of 2,100 km², measuring around 100 km × 30 km. According to the 2000 census, Manus Island had a population of approximately 43,000. Lorengau, the capital of Manus Province, is located on the island. Momote Airport, the terminal for Manus Province, is located on nearby Los Negros Island. A bridge connects Los Negros to Manus Island and the province capital of Lorengau.

Manus Island is covered in rugged jungles, which can be broadly described as lowland tropical rain forest. The highest point on Manus Island is Mt. Dremsel 718 metres (2,356 feet) above sea level at the centre of the south coast. Manus is volcanic in origin and probably broke through the ocean's surface in the late Miocene, 8–10 million years ago. The substrate of the island is either directly volcanic or from uplifted coral limestone.

Manus Island is home to the Emerald green snail, whose shells are harvested to be sold as jewellery.