Arne Odd Johnsen (3 December 1909 – 9 July 1985) was a Norwegian medieval and economic historian.
He was born in Asker as the son of historian Oscar Albert Johnsen (1876–1954) and Anna Evie Tollefsen (1877–1944).
Between 1937 and 1939 he studied medieval history at École des Chartes, Sorbonne and Collège de France.
[1] In 1945 he published his thesis Studier vedrørende kardinal Nicolaus Brekespears legasjon til Norden,[2] about Cardinal Nicolas Breakspear, later known as Pope Adrian IV.
Johnsen became known for his endeavor to publish source documents from medieval and early modern times.