Christiansø is an island in Denmark that serves as the primary reference point for the Ertholmene archipelago. Located approximately 18 kilometres (11 mi) northeast of Gudhjem, Bornholm, the area includes Denmark's easternmost point.
The archipelago has a total area of 39 hectares and its name is derived from the Danish word for "pea islands." While Christiansø is the largest island in the group, only two of the islands—Christiansø and Frederiksø—are inhabited, with a combined permanent population of 90 residents.