Jonas Jansen

Jens Jonas Schroeter Jansen (19 September 1900 – 26 October 1975) was a Norwegian archivist.

He was born in Bærum as a son of vicar Jens Jonas Elstrand Jansen (1844–1912) and Jenny Therese Schroeter (1863–1942), and brother of Einar Jansen. In 1937 he married Hjørdis Sofie Berg. with a master's thesis on the Treaty of Björkö.

He worked in the National Archives of Norway from 1936 to 1956, and also worked as a consultant in the Ministry of Foreign Affairs from 1949 to 1952. He was then the manager of Norsk Historisk Kjeldeskrift-Institutt from 1953 to 1970. He is also known as a co-editor of the biographical dictionary Norsk Biografisk Leksikon from 1954. He chaired the union Arkivarforeningen from 1938 to 1947 and was a board member of Kjeldeskriftfondet from 1940 to 1945 and of the Norwegian Genealogical Society from 1949.