Seiland (Sami: Sievju) is an island in the southwest of Hammerfest in Finnmark county. The island is divided between the municipalities of Hammerfest, Alta and Kvalsund and has an area of 559 square kilometres (216 sq mi). This makes it the eighth largest island in mainland Norway.
Archeological excavations have shown that people have lived on Seiland for 7000 years, but today there are only people living in Kårhamn, Hønseby, Eidvågen, Fiskebukta, Survika, Altneset and Hakkstabben.
Since 2006, large parts of the island constitutes Seiland National Park.
There are two glaciers on Seiland; Seilandsjøkelen and Nordmannsjøkelen.