Iwate Prefecture (岩手県, Iwate-ken; Japanese pronunciation: [iꜜ.wa.te, i.wa.teꜜ.keɴ]) is a prefecture of Japan located in the Tōhoku region of Honshu. It is the second-largest Japanese prefecture (behind Hokkaido) at 15,275 square kilometres (5,898 sq mi), with a population of 1,165,886 (as of July 1, 2023). Iwate Prefecture borders Aomori Prefecture to the north, Akita Prefecture to the west, and Miyagi Prefecture to the south.

Morioka is the capital and largest city of Iwate Prefecture; other major cities include Ichinoseki, Ōshū, and Hanamaki. Located on Japan's Pacific Ocean coast, Iwate Prefecture features the easternmost point of Honshu at Cape Todo, and shares the highest peaks of the Ōu Mountains—the longest mountain range in Japan—at the border with Akita Prefecture. Iwate Prefecture is home to famous attractions such as Morioka Castle, the Buddhist temples of Hiraizumi including Chūson-ji and Mōtsū-ji, the Fujiwara no Sato movie lot and theme park in Ōshū, and the Tenshochi park in Kitakami known for its huge, ancient cherry trees. Iwate has the lowest population density of any prefecture outside Hokkaido, 5% of its total land area having been designated as national parks.

There are several theories about the origin of the name "Iwate", but the most well known is the tale Oni no tegata, which is associated with the Mitsuishi or "Three Rocks" Shrine in Morioka. These rocks are said to have been thrown down into Morioka by an eruption of Mt. Iwate. According to the legend, there was once a devil who often tormented and harassed the local people. When the people prayed to the spirits of Mitsuishi for protection, the devil was immediately shackled to these rocks and forced to make a promise never to trouble the people again. As a seal of his oath, the devil made a handprint on one of the rocks, giving rise to the name Iwate, its direct translation being "rock hand". Even now after a rainfall, it is said that the devil's hand print can still be seen there.

There are many present-day cultural foods popularly eaten in Iwate Prefecture, some of which include walnuts, wanko soba (meaning "bowl noodles") and hittsumi-jiru (meaning "pull and tear", in reference to the way the dough is pulled and torn into oval shapes before being turned into noodles). Iwate's prefectural capital Morioka is also popular for its apples, blooming in May and ready for harvest from September to November.

Japanese poet Matsuo Bashō visited Iwate and wrote about it in the journey described in his major work Oku no Hosomichi. He was especially inspired by the town of Hiraizumi.

While the entire island of Honshū was claimed by the Japanese, or Yamato, government from earliest times, the imperial forces were unable to occupy any part of what would become Iwate until 802 when two powerful Emishi leaders, Aterui and More, surrendered at Fort Isawa.

The area now known as Iwate Prefecture was inhabited by the Jōmon people who left their artifacts throughout the prefecture. For example, a large number of burial pits from the Middle Jōmon Period (2,800–1,900 BC) have been found in Nishida. Various sites from the Late Jōmon Period (1,900–1,300 BC) including Tateishi, Makumae and Hatten contain clay figurines, masks and ear and nose shaped clay artifacts. The Kunenbashi site in Kitakami City has yielded stone "swords", tablets and tools as well as clay figurines, earrings and potsherds from the Final Jōmon Period (1,300–300 BC).

The earliest mention of a Japanese presence dates to about 630 when the Hakusan Shrine was said to have been built on Mt. Kanzan in what is now Hiraizumi. At this time various Japanese traders, hunters, adventurers, priests and criminals made their way to Iwate. In 712 the province of Mutsu, containing all of Tōhoku, was divided into Dewa Province, the area west of the Ōu Mountains and Mutsu Province. In 729 Kokuseki-ji Temple was founded in what is now Mizusawa Ward, Oshu City by the itinerant priest Gyōki.