Hidra[1] (historically spelled Hitterø) is the largest island in Agder county, Norway.

The 20.8-square-kilometre (8.0 sq mi) island lies in Flekkefjord Municipality, south of the mainland coast, separated by the 350-metre (1,150 ft) wide Hidrasund strait and the Listafjorden.

[2] The island has about 500 residents (in 2015), mostly living on the west side in Kirkehavn, where Hidra Church is located.

In 2007, the government of Norway studied the possibility of building an undersea tunnel to connect the island to the mainland without a ferry, but it was deemed to be too costly for the small benefit.

The island is divided nearly in two halves by the Rasvågfjorden, and the Eie Canal was built through the remaining isthmus so that small boats can pass all the way through.