Hokkaidō (Japanese: 北海道, Hepburn: Hokkaidō, literally “Northern Sea Circuit” or “Northern Sea Region”), officially Hokkaidō Circuit Prefecture, is the second largest island of Japan and comprises the largest and northernmost prefecture. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel.
The largest city on Hokkaidō is its capital, Sapporo, which is also its only ordinance-designated city. Sakhalin lies about 43 kilometers (26 mi) to the north of Hokkaidō, and to the east and northeast are the Kuril Islands, which are administered by Russia, though the four most southerly are claimed by Japan. Hokkaidō was formerly known as Ezo, Yezo, Yeso, or Yesso.