Janet Loxley Lewis (August 17, 1899 – December 1, 1998) was an American novelist, poet, and librettist. She was considered one of the finest American literary figures of the 20th century.

Lewis was born in Chicago, Illinois to Elizabeth Taylor Lewis and Edwin H. Lewis. She was a graduate of the University of Chicago, where she was a member of a literary circle that included Glenway Wescott, Elizabeth Madox Roberts, and her future husband Yvor Winters. She joined the University of Chicago Poetry Club on the advice of Winters, who was a founding member and, at the time, secretary. Lewis taught at both Stanford University in California and the University of California at Berkeley.

She wrote The Wife of Martin Guerre (1941) which is the tale of one man's deception and another's cowardice. Her first novel was The Invasion: A Narrative of Events Concerning the Johnston Family of St. Mary's (1932). Other prose works include The Trial of Soren Qvist (1947), The Ghost of Monsieur Scarron (1959), and the volume of short fiction, Good-bye, Son, and Other Stories (1946).

Lewis was also a poet, and concentrated on imagery, rhythms, and lyricism to achieve her goal. Among her works are The Indians in the Woods (1922), and the later collections Poems, 1924–1944 (1950), and Poems Old and New, 1918–1978 (1981). She also collaborated with Alva Henderson, a composer for whom she wrote three libretti and several song texts.

She married the American poet and critic Yvor Winters in 1926. Together they founded Gyroscope, a literary magazine that lasted from 1929 until 1931.

Lewis was elected a Fellow of the American Academy of Arts and Sciences in 1992. She died at her home in Los Altos, California, in 1998, at the age of 99.