From the English Wikipedia page 
The National Library of Norway (Norwegian: Nasjonalbiblioteket) was established in 1989. Its principal task is "to preserve the past for the future". The library is located both in Oslo and in Mo i Rana. The building in Oslo was restored and reopened in 2005.
Prior to the existence of the National Library, the University Library of Oslo was assigned the tasks that normally falls to a national library.
The Norwegian ISBN Agency, responsible for assigning ISBNs with prefix 82- and 978-82-, is part of the National Library of Norway. The National Library is also responsible for legal deposits made from publishers in Norway. All material is to be submitted free of charge.
More information on the Norwegian Wikipedia page 
The website, in Norwegian, is