Shimonoseki (Japanese: 下関市, Hepburn: Shimonoseki-shi) is a city located in Yamaguchi Prefecture, Japan.

It has prospered since ancient times as the gateway to Honshu island from the Asian continent, including Kyushu, China, and the Korean peninsula.

According to the Nihon Shoki, the semi-legendary Emperor Chuai constructed a palace at the location of what is now the Shimonoseki city hall during the Kofun period.

During the Genpei War, the Heike and Genji fought at the Battle of Dan-no-ura near the present Kanmon Bridge.

During the Muromachi period, the powerful Ōuchi clan was shugo of both Nagato and Buzen Province in Kyushu and thus controlled trade and diplomatic missions from Ming China and Joseon Korea.

In February 1691, German explorer Engelbert Kaempfer visited the town as part of his two-year stay in Japan, and described it as having around 400 to 500 houses, and as a major port in the region for supplying ship provisions.

Shimonoseki has a mayor-council form of government with a directly elected mayor and a unicameral city council of 34 members.

In terms of national politics, the city is part of the Yamaguchi 3rd district of the lower house of the Diet of Japan.

Having prospered as a port city, Shimonoseki has long had a thriving industry related to shipping, trade, and finance.