Izu Ōshima is an inhabited volcanic island in the Izu archipelago in the Philippine Sea, off the coast of Honshu, Japan, 22 km (14 mi) east of the Izu Peninsula and 36 km (22 mi) southwest of Bōsō Peninsula. As with the other islands in the Izu Island group, Izu Ōshima forms part of the Fuji-Hakone-Izu National Park. Izu Ōshima, at 91.06 km2 (35.16 sq mi) is the largest and closest of Tokyo's outlying islands, which also include the Ogasawara Islands.

The Izu Islands are a group of volcanic islands stretching south and east from the Izu Peninsula of Honshū, Japan. Administratively, they form two towns and six villages; all part of Tokyo Prefecture. The largest is Izu Ōshima, usually called simply Ōshima.