The municipality had excellent natural conditions for building harbours, it became the site of Norsk Hydro's plant at Herøya and the Dalen Portland (now part of the Norcem corporation) concrete factory just outside Brevik.

More recently, a major industry in the area is Heistad Fabrikker, which makes products for diabetics.

Isola has two factories in this area where bitumen-based products and steel roofing tiles are manufactured.

During the 1960s, there were many municipal mergers across Norway due to the work of the Schei Committee.

[6] The municipality (originally the parish) is named after the Eidangerfjorden (Old Norse: Eiðangr) since the historic Eidanger Church was built at the head of the fjord.

[8] The municipal council (Herredsstyre) of Eidanger was made up of representatives that were elected to four year terms.