Siberut is the largest and northernmost of the Mentawai Islands, lying 150 kilometres west of Sumatra in the Indian Ocean. A part of Indonesia, the island is the most important home for the Mentawai people. The western half of the island was set aside as the Siberut National Park in 1993. Much of the island is covered with rainforest, but is subject to commercial logging.
Smaller islands adjacent to Siberut include Karamajet and Masokut which lie in the Bungalaut strait at the south of the island.
The island is known for its range of primates, including the Kloss gibbon (Hylobates klossii), pig-tailed langur (Simias concolor), Mentawai langur (Presbytis potenziani) and Mentawai macaque (Macaca pagensis).
Siberut was affected by the 2004 Indian Ocean earthquake tsunami, but without any known loss of human life. One report stated that the island may have been raised up to two metres by the earthquake.