Sakhalin is an island at the east coast of Asia. It is a part of Sakhalin region and the largest island in the Russian Federation. Sakhalin is washed by the Sea of Okhotsk and the Sea of Japan. From continental Asia it is separated by the Gulf of Tartary (in the narrowest part, called Nevelskoyi Strait, has a 7.3 km width and freezes over in winter) and from the Japanese island of Hokkaido – by the La Perouse Strait.

The island is elongated from Cape Crillon in the south to Cape Elizabeth in the north. Its length is 948 km, it’s width is from 26 km (Belt isthmus) up to 160 km (at latitude of Lesogorskoye village), its total area is 76.4 thousand km².