Hisingen is the fifth-largest island of Sweden, with an area of 199 km2 (77 sq mi). It is a river island, formed by the split of the Göta Älv at Bohus, and is defined to the east and south by the main arm of that river, to the north by the smaller arm, and to the west by the Kattegat. The southern part of Hisingen is extensively urbanised, representing the northern suburbs of the city of Gothenburg. The island is divided between the historical provinces of Västergötland and Bohuslän, but lies entirely within the modern county of Västra Götaland.

A river island is any exposed landmass surrounded by river water. Properly defined, it excludes shoals between seasonally varying flows and may exclude semi-coastal islands in river deltas such as Marajó.