Izu (伊豆国; -no kuni) was a province of Japan including the Izu Peninsula that is today part of Shizuoka prefecture and the Izu Islands that are now part of Tokyo. Izu bordered on Sagami and Suruga Provinces. Another name was Zushū. Prior to 680 A.D., it was part of Suruga province. From that year until the Edo period, Izu included three districts: Tagata, Kamo and Naka. During the Edo period, Kimisawa became the fourth district of Izu.

The First Shrine (Ichinomiya) of Izu was the Mishima Shrine. The Ninomiya Hachimangu and the Asama Shrine, which were also in Mishima, were the second and third. In addition, Mishima was the location of the Provincial Temple, or Kokubunji.

During the Sengoku period, Izu was typically dominated by whoever ruled the Kanto provinces of Sagami and Musashi, including the Hojo clan and later the Tokugawa shoguns themselves.

Izu was a major setting for the novel (and miniseries) Shogun