Ruhnu (Swedish: Runö; Latvian: Roņu sala; Livonian: Rūnõmō) is an Estonian island in the Gulf of Riga in the Baltic Sea.

The island has been designated an Important Bird Area (IBA) by BirdLife International because it supports significant numbers of long-tailed ducks and velvet scoters, both wintering and on passage.

It probably did not precede the Northern Crusades at the beginning of the 13th century, when the indigenous peoples of all the lands surrounding the Gulf of Riga were converted to Christianity and subjugated to the Teutonic Order.

Ruhnu was controlled by the Kingdom of Sweden (1621–1708, formally until 1721) and after that by the Russian Empire until World War I, when it was occupied by Imperial German armed forces (1915–1918).

Under the tsarist Russian rule in the 18th–19th century the island had de facto independence in most affairs, though designated as crown land.

In August 1944, shortly before the Red Army of the Soviet Union reoccupied Estonia, the remaining population of the island, except for two families, fled by ship to Sweden.

[10] A herd of fifty highland cattle were introduced to Ruhnu in 2013, in an attempt to restore the semi-natural coastal meadows in the southwestern part of the island.

[11] In the spring of 2006, a 150-kilogram (330 lb) brown bear arrived on Ruhnu via an ice floe across the Gulf of Riga from the mainland of Latvia, some 40 km (25 mi) away.

The bear's journey and resettlement on the island became a highly publicized media sensation in both the Estonian and Latvian press, as Ruhnu has been devoid of any large carnivores for many centuries.