Honshu (本州, Honshū^?, literally "Main Province") ([hoɴɕuː] ( listen)) is the largest island of Japan. The nation's main island, it is south of Hokkaido across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyushu across the Kanmon Strait. It is the seventh largest island in the world, and the second most populous after Java in Indonesia.

It has a population of 103 million in 2005, (98,352,000 as of 1990; in 1975 it was 89,101,702), mostly concentrated in the available lowlands, notably in the Kantō plain where 25% of the total population reside in the Greater Tokyo Area, which includes Tokyo and Yokohama, Kawasaki, Saitama and Chiba cities. Most of the nation's industry is located along the belt running from Tokyo along Honshu's southern coastal cities, including Kyoto, Osaka, Nagoya, Kobe, and Hiroshima, part of the Taiheiyo Belt.

The economy along the northwestern coast by the Sea of Japan is largely fishing and agriculture;Niigata is noted as an important producer of rice. The Kantō and Nōbi plains produce rice and vegetables. Yamanashi is a major fruit-growing area, and Aomori is famous for its apples.