The Izu peninsula is a large mountainous peninsula with a deeply indented coastline to the west of Tokyo on the Pacific coast of the island of Honshu, Japan. Formerly known as Izu Province, Izu peninsula is now a part of Shizuoka Prefecture. The peninsula has an area of 1,421.24 km2 (548.74 sq mi) and its estimated population in 2005 was 473,942 people. The peninsula’s populated areas are located primarily on the north and east.

Izu Province was a province of Japan in the area of Shizuoka Prefecture. Izu bordered on Sagami and Suruga Provinces. Its abbreviated form name was Zushū (豆州).