Sakhalin (səkhəlyēn´), formerly Saghalien (sägälyĕn´), island (c.29,500 sq mi/76,400 sq km), off the coast of Asian Russia, between the Sea of Okhotsk and the Sea of Japan; separated from the Russian mainland on the west by the Tatar Strait and from Hokkaido, the northernmost island of Japan, by the Soya Strait. With the Kuril Islands it forms the Sakhalin region (1995 est. pop. 673,100) of the Russian Far East. Yuzhno-Sakhalinsk, near the S end of Sakhalin, is the oblast's capital.
Two parallel mountain ranges, separated by a central valley, run the length of this elongated and forested island. The climate is severe, but grains, beets, and potatoes are successfully grown in the south. Lumbering, offshore gas production, herring fishing, and paper milling are the principal industries. There are oil fields in the northeast and pipelines run to Nikolayevsk and Komsomolsk Amur on the mainland; offshore oil and gas fields are being developed, and liquefied natural gas is shipped from Prigorodnoye, SE of the capital. Despite their small size, the coal and iron deposits are vital to Asian Russia, where these minerals are scarce. Coastal shipping is also important to Sakhalin's economy. The island's population is predominantly Russian, with the indigenous tribe of Gilyaks the largest minority.
Sakhalin was explored by Russians in the 17th cent. and subsequently colonized by Russia and Japan in the 18th and 19th cent. It was under joint Russo-Japanese control (formalized by the Treaty of Shimoda, 1855) until it passed entirely to Russia in 1875, when Japan obtained the Kuril Islands in return. Sakhalin became a czarist place of exile. By the Treaty of Portsmouth (1905), Russia retained the portion of Sakhalin north of lat. 50° N and Japan obtained the remainder. The Japanese territory was named Karafuto, and this name was sometimes applied to the whole island. Both countries colonized extensively and reduced the native population to a minority.
After World War II the Japanese holdings were transferred to the USSR and nearly all the Japanese population was repatriated. In an agreement signed in 1951 with the USSR, Japan renounced all claims to Sakhalin. In the hope of attracting foreign investment, the island's parliament declared the island a free trade zone in 1990, and Sakhalin residents began trading with the Japanese. In 1995 the northern city of Neftegorsk was leveled by an earthquake; nearly 2,000 people died. The beginning of the 21st cent. brought the development of offshore oil and gas fields and a consequent economic boom.