Gunung Leuser National Park is a national park covering 7,927 km2 in northern Sumatra, Indonesia, straddling the border of Aceh and North Sumatra provinces, a fourth portion and three-fourths portion, respectively. The national park, settled in the Barisan mountain range, is named after Mount Leuser (3,119 m), and protects a wide range of ecosystems. An orangutan sanctuary at Bukit Lawang is located within the park. Together with Bukit Barisan Selatan and Kerinci Seblat National Parks, it forms a World Heritage Site, the Tropical Rainforest Heritage of Sumatra.

Sumatra is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the sixth-largest island in the world at 475,807.63 km2 (182,812 mi.2), including adjacent islands such as the Simeulue, Nias, Mentawai, Enggano, Riau Islands, Bangka Belitung and Krakatoa archipelago.