Ruhnu is an Estonian island in the Gulf of Riga in the Baltic Sea. Its territory of 11.9 square kilometres (4.6 sq mi) is administratively part of Saare maakond (county). Ruhnu lies geographically closer to the coast of Courland on the mainland of Latvia than it is to any point in rest of Estonia. With less than 150 official residents, the Ruhnu vald (parish) has the smallest population of Estonia's 79 municipalities. Before 1944, it was for centuries populated by ethnic Swedes and traditional Swedish law was used.

The Estonian Swedes, or Estonia-Swedes, or "Coastal Swedes" are a Swedish-speaking minority traditionally residing in the coastal areas and islands of what is now western and northern Estonia. During World War II, almost all of the remaining Swedish-speaking minority escaped from the Soviet invasion of Estonia and fled to Sweden in 1944. Only the descendants of a few individuals who stayed behind are permanent residents in Estonia today.