Tromøya or Tromøy is the largest island in Southern Norway. The 28.6-square-kilometre (11.0 sq mi) island is entirely located in the municipality of Arendal in Agder county, Norway. The island has about 5,300 residents which gives it a population density of about 185 inhabitants per square kilometre (480/sq mi). The island is located directly across the harbor from the town of Arendal. The highest point on the island is the 95-metre (312 ft) tall Vardåsen. The island is separated from the mainland to the north by the Tromøysundet strait and it is separated from the island of Hisøya to the southwest by the Galtesundet strait.

Arendal is a municipality in Agder county in southeastern Norway. Arendal belongs to the region of Sørlandet. The administrative centre of the municipality is the city of Arendal. Some of the notable villages in Arendal include Rykene, Eydehavn, Færvik, Strengereid, Kongshavn, Kilsund, Brattekleiv, Torsbudalen, Longum, Saltrød, Staubø, Vrengen, and Kolbjørnsvik. The offices of UNEP/GRID-Arendal are also located in the city of Arendal.