Carl Johan Sverdrup Marstrander (1883-1965) was a Norwegian linguist, known for his work on the Irish language. His works, largely written in Norwegian, on the Celtic and Norse components in Norwegian culture, are considered important for modern Norway.
He was a student of Sophus Bugge and Alf Torp, and spent time in Ireland from 1907, studying on Great Blasket Island with Tomás Ó Criomhthain, and then teaching at the School of Irish Learning in 1910. From 1913 to 1954 he was Professor in Celtic languages at the University of Oslo. During the German occupation of Norway he was jailed several times. He influenced later linguists, including Alf Sommerfelt and Carl H. J. Borgstrøm.
In 1913 he began the actual publication of the long-projected historical Dictionary of the Irish Language. He is also known for his writings on the history of the Isle of Man,  and for securing support and recognition for the Manx historian J. J. Kneen. He made pioneering sound recordings of the Manx language, at a time when few fluent native speakers survived.
- Diarmuid Ó Giolláin, Locating Irish Folklore: Tradition, Modernity, Identity (2000), pp. 125.
- Oskar Bandle, Kurt Braunmüller. The Nordic Languages: an international handbook of the history of the North Germanic languages (2002), p. 130.
- Professor Marstrander's contribution to Manx History