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.