Norway doesn't have a single "main island" in the same way that the UK has Great Britain. Norway is made up of a mainland and a large number of islands.

The largest island in Norway is Hinnøya. It's part of the Vesterålen archipelago in Nordland county.

However, it's more common to refer to the Scandinavian Peninsula as the "mainland" of Norway. This is where the majority of the population and landmass is located.