In 1931, Haugen joined the faculty of the
University of Wisconsin–Madison. He would spend more than thirty years in Madison, finally leaving in 1962 to accept a position at
Harvard University. Before his departure, he recruited Norwegian scholar and
Hamsun expert
Harald Næss to Wisconsin to serve as his successor. At Harvard, Haugen was made Victor S. Thomas Professor of Scandinavian and Linguistics and remained on faculty until his retirement in 1975. Perhaps his most important work was
The Norwegian language in America: A Study in Bilingual Behavior (). In addition to several important works within these fields, he wrote the authoritative work on the dialect of his ancestral home of Oppdal and a book entitled
The Ecology of Language, with which he pioneered a new field of linguistics later called
Ecolinguistics. Einar Haugen also wrote
Norwegian English Dictionary/Norsk engelsk ordbok (). His last book was a biography of the Norwegian virtuoso violinist
Ole Bull co-written with his daughter, Camilla Cai. ==Memorials==