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. It has a wild, mountainous outer (western) side facing the Atlantic, and a mild and lush inner (eastern) side. The island is located 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.

Senja is a municipality in Troms county, Norway. It was established on 1 January 2020 when the municipalities of Berg, Lenvik, Torsken, and Tranøy were merged into one municipality. It is located in the traditional district of Hålogaland. The administrative centre of the municipality is the town of Finnsnes. The municipality includes all of the island of Senja, the smaller surrounding islands, and part of the mainland between the Gisundet strait and the Malangen fjord.