Martin Fredrik Böök (May 12, 1883 in Kristianstad – December 2, 1961 in Copenhagen) was a Swedish professor of literary history at Lund University 1920-24, a literary critic and writer. He wrote biographies and books on Swedish literature. In 1907, Fredrik married Tora Olsson. Their son Klas Böök (born 1909) became head of the Bank of Sweden and later an ambassador.
Alongside Henrik Schück, Böök was for decades the most influential (and feared) Swedish literature scholar and critic. He reviewed books for the newspaper Svenska Dagbladet, succeeding Oscar Levertin. In 1922 he became a member of the Swedish Academy, seat 10. During World War II, Böök actively supported the cause of Germany as a belligerent power. After the war he lost his dominating role in the literary field. His biography was written in 1994 by Svante Nordin.