Senja (Norwegian) or Sážžá (Northern Sami) is an island in Senja Municipality in Troms county, Norway in northern Europe. With an area of 1,586.3 square kilometres (612.5 sq mi), it is the second largest island in Norway (outside of the Svalbard archipelago). It has a wild, mountainous outer (western) side facing the Atlantic, and a mild and lush inner (eastern) side. The island is located entirely within Senja Municipality, which was established on 1 January 2020. The island of Senja had 7,864 inhabitants as of 1 January 2017. Most of the residents live along the eastern coast of the island, with Silsand being the largest urban area on the island. The fishing village of Gryllefjord on the west coast has a summer-only ferry connection to the nearby island of Andøya: the Andenes–Gryllefjord Ferry.

The island sits northeast of the Vesterålen archipelago, surrounded by the Norwegian Sea to the northwest, the Malangen fjord to the northeast, the Gisundet strait to the east, the Solbergfjorden to the southeast, the Vågsfjorden to the south, and the Andfjorden to the west. Ånderdalen National Park is located in the southern part of the island.