Honshu (本州, Honshū, pronounced [hoɰ̃ꜜɕɯː] (listen); "Main island/Main province") is the largest and most populous main island of Japan.^[3][4] located south of Hokkaido across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyushu across the Kanmon Straits. The island separates the Sea of Japan, which lies to its north and west, from the North Pacific Ocean to the south and east. It is the 7th largest island in the world, and the 2nd most populous after the Indonesian island of Java.^[5][6][7]

Honshu had a population of 104 million as of 2017,^[2] mostly concentrated in the coastal areas and plains. Approximately 30% of the total population resides in the Greater Tokyo Area on the Kantō Plain. As the historical center of Japanese cultural and political power, the island includes several past Japanese capitals, including Kyoto, Nara, and Kamakura. Much of the island's southern shore forms part of the Taiheiyō Belt, a megalopolis that spans several of the Japanese islands.

Most of Japan's industry is located in a belt running along Honshu's southern coast, from Tokyo to Nagoya, Kyoto, Osaka, Kobe, and Hiroshima; by contrast, the economy along the northwestern Sea of Japan coast is largely based on fishing and agriculture.^[8] The island is linked to the other three major Japanese islands by a number of bridges and tunnels. Its climate is humid and mild.

The island is roughly 1,300 km (810 mi) long and ranges from 50 to 230 km (31 to 143 mi) wide, and its total area is 227,960 km2 (88,020 sq mi),^[1] making it slightly larger than the island of Great Britain 209,331 km2 (80,823 sq mi).^[9] Its land area has been increasing with land reclamation and coastal uplift in the north due to plate tectonics with a convergent boundary. Honshu has 10,084 kilometres (6,266 mi) of coastline.^[4]

Mountainous and volcanic, Honshu experiences frequent earthquakes (the Great Kantō earthquake heavily damaged Tokyo in September 1923, and the earthquake of March 2011 moved the northeastern part of the island by varying amounts of as much as 5.3 m (17 ft)^[10][11] while causing devastating tsunamis). The highest peak is the active volcano Mount Fuji at 3,776 m (12,388 ft), which makes Honshu the world's 7th highest island. There are many rivers, including the Shinano River, Japan's longest. The Japanese Alps span the width of Honshu, from the 'Sea of Japan' coast to the Pacific shore. The climate is generally humid subtropical in western Japan and humid continental in the north.

Honshu is connected to the islands of Hokkaido, Kyushu and Shikoku by tunnels and bridges. Three bridge systems have been built across the islands of the Inland Sea between Honshu and Shikoku (Akashi Kaikyō Bridge and the Ōnaruto Bridge; Shin-Onomichi Bridge, Innoshima Bridge, Ikuchi Bridge, Tatara Bridge, Ōmishima Bridge, Hakata–Ōshima Bridge, and the Kurushima-Kaikyō Bridge; Shimotsui-Seto Bridge, Hitsuishijima Bridge, Iwakurojima Bridge, Yoshima Bridge, Kita Bisan-Seto Bridge, and the Minami Bisan-Seto Bridge), the Seikan Tunnel connects Honshu with Hokkaido, and the Kanmonkyo Bridge and Kanmon Tunnel connects Honshu with Kyushu.

Its population is about 127 million people, according to a 2019 estimate.

The island is divided into five nominal regions and contains 34 prefectures, including metropolitan Tokyo. Administratively, some smaller islands are included within these prefectures, notably including the Ogasawara Islands, Sado Island, Izu Ōshima, and Awaji Island.

The regions and its prefectures are:

Most of Japan's tea and silk is from Honshu. Fruits, vegetables, grains, rice and cotton are grown in Honshu.^[12] 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. Rare species of the lichen genus Menegazzia are found only in Honshu.^[13]

Yields of zinc, copper, and oil have been found on Honshu.^[12]