Rishiri Island is a volcanic island in the Sea of Japan off the coast of Hokkaido, Japan. Administratively the island is part of Hokkaido Prefecture, and is divided between two towns, Rishiri and Rishirifuji. The island is formed by the cone-shaped extinct volcanic peak of Mount Rishiri. Along with Rebun Island and the coastal area of the Sarobetsu Plain, Rishiri forms the Rishiri-Rebun-Sarobetsu National Park. The main industries of Rishiri are tourism and fishing. The island is about 63 kilometres (39 mi) in circumference and covers 183 square kilometres (71 sq mi). The island has a population of 5,102 residents.

The Sea of Japan (see below for other names) is the marginal sea between the Japanese archipelago, Sakhalin, the Korean Peninsula, and the mainland of the Russian Far East. The Japanese archipelago separates the sea from the Pacific Ocean. Like the Mediterranean Sea, it has almost no tides due to its nearly complete enclosure from the Pacific Ocean. This isolation also affects faunal diversity and salinity, both of which are lower than in the open ocean. The sea has no large islands, bays or capes. Its water balance is mostly determined by the inflow and outflow through the straits connecting it to the neighboring seas and the Pacific Ocean. Few rivers discharge into the sea and their total contribution to the water exchange is within 1%.