Basilan (bäsēˈlän) [key], island, 494 sq mi (1,279 sq km), northernmost and largest of the Sulu Archipelago, the Philippines. It is closely associated with the city of Zamboanga on Mindanao island, just across the 10-mi (16-km) wide Basilan Strait. Major sources of income are sea products, coconut, timber, and rubber. The Univ. of the Philippines maintains a vast rubber plantation there. With neighboring islets, Basilan forms the Basilan island group. The inhabitants are chiefly Muslim, and the island has been the scene of fighting between government troops and Muslim rebels.