Hiiumaa is the main island of Hiiu County, called Hiiumaa or Hiiu maakond in Estonian. The Swedish and German name of the island is Dagö (day island), Dagø in Danish — a calque of its old Finnish name Päivänsalo (day island); compare Ösel (Yösalo - night island) for Saaremaa. In modern Finnish it is called Hiidenmaa, literally hiisi's land. In Old Gutnish it was Dagaiþ (day isthmus), from which the local North Germanic name "Daë" is derived.
Archaeological evidence of the first human settlement in Hiiumaa dates to as early as the 4th century BC. The first documented record of the island of Dageida was made by contemporary chroniclers in 1228, at the time when Hiiumaa, along with the rest of Estonia, had been conquered by Germanic crusaders. In 1254, Hiiumaa was divided between the Bishopric of Ösel-Wiek and the Livonian branch of the Teutonic Order, who were also partly acting on behalf of the Hanseatic League.
The island was part of Swedish Estonia from 1563-1710, after which it passed to the Russian Empire as part of the Governorate of Estonia. Most of the island's previously numerous Swedish-speaking population emigrated or were "Estonianised" during the period of Imperial Russian rule.
Hiiumaa was occupied during World War I by the Imperial German Army, and became a part of independent Estonia after the war. It was annexed by the Soviet Union in 1940, by Nazi Germany in 1941, and by the Soviets again in 1944. It was then a part of the Estonian Soviet Socialist Republic until the Soviet Union's collapse in 1991. Since then, it has been a part of independent Estonia.
Road transport from Estonian mainland to Hiiumaa involves a 90-minute (28km) ferry crossing from Rohuküla to Heltermaa, which is 25km by road from Kärdla. There are about 10 ferry departures a day. In the summer weekends, getting car space on the ferry usually requires advance booking. There are about 2 scheduled buses a day between Tallinn (the capital of Estonia) and Kärdla.
Hiiumaa is served by Kärdla Airport, with regular flights to Tallinn.