Magnus Bernhard Olsen (Arendal, 28 November 1878 – Oslo, 16 January 1963) was a Norwegian linguist and a professor in Norse philology at the University of Oslo from 1908 to 1948. His writings on Norse paganism and interpretations of the names of Norwegian farms and other placenames were influential, and his contribution to runology, particularly Norwegian runology, was considerable.
After finishing school in 1896, Olsen studied at the University of Oslo and received his Candidatus philologiæ degree in 1903. From 1899 onwards, he worked as an assistant at the University Library; from 1902 he was assistant to the almost blind Sophus Bugge. After 1904 he received a stipend. In 1908, at the age of 30, he was chosen to succeed Bugge as Professor of Old Norse and Icelandic Language and Literature; in 1921 the department was renamed Norse Philology.
During his lifetime, Olsen was one of the most prominent and best known scholars in his field. His publications included 7 volumes of Eddic and skaldic poetry with commentary, and also several volumes on runic inscriptions: after assisting Sophus Bugge in completing publication of the inscriptions in the Elder Futhark, he published the first 5 volumes on the inscriptions in the Younger Futhark. Although he took magical interpretations of runic inscriptions further than do later scholars, they were always on a reasoned basis. He assisted as joint editor and editor of 3 volumes in the completion of Oluf Rygh's Norske Gaardnavne. He is best known for the framework he established for dating placenames and relating them to religion and society in the pre-Christian era, which he presented in two books, Hedenske Kulturminder i Norske Stedsnavne ("Heathen Cultural Remnants in Norwegian Placenames" - 1915) and Ættegård og Helligdom, Norske Stednavn Sosialt og Religionshistorisk Belyst (1926, translated into English as Farms and Fanes of Ancient Norway: The Place-Names of a Country Discussed in Their Bearings on Social and Religious History, 1928). Hva våre stedsnavn lærer oss ("What Our Placenames Teach Us" - 1934) is a succinct introduction to the subject.
Olsen founded the journal Maal og Minne in 1909, and edited it for 40 years. His article in the first issue, "Fra gammelnorsk myte og kultus," was in itself an important contribution to the study of Germanic religion, interpreting "Skírnismál" in terms of the hieros gamos. His inaugural lecture in 1908 had had the same title and topic. In 1941, during World War II, Magnus Olsen was chosen dekanus (Dean) at the university after Francis Bull was arrested. In 1952 he was honoured with a state pension.
He became a Commander of the Order of St. Olav in 1945. He was a member of the Norwegian Academy of Science and Letters from 1904, a member of the Royal Norwegian Society of Sciences and Letters, and a Knight in the Icelandic Order of the Falcon and the Swedish Order of the Polar Star.
In 1912 he married Gjertrud Mathilde Kjær, daughter of Albert Kjær, librarian at the Oslo Public Library and head librarian at the University Library.Ludvig Holm-Olsen, professor of Old Norse philology at the University of Bergen, was his nephew.