Polish-born American author and social scientist best known for his popular books on Yiddish (Yiddish language) and for his comic novels featuring the immigrant night-school student Hyman Kaplan.

At age three Rosten immigrated with his parents to Chicago. He graduated from the University of Chicago in 1930 and received his Ph.D. in 1937. After working as a screenwriter and holding a series of wartime government-information jobs, he joined the staff of Look magazine in New York in 1949, where he worked until 1971; he also lectured at Columbia University.

In 1937 Rosten (as Leonard Q. Ross) published The Education of H*Y*M*A*N K*A*P*L*A*N; the book, based on the author's experiences teaching English to immigrants, is full of puns and malapropisms (malapropism) based on the fractured English of the cherubic, naive Kaplan, for whom the plural of “sandwich” is “delicatessen.” The novel was acclaimed for its high spirits and its comic mastery of Yiddish-inflected English. Two sequels, The Return of H*Y*M*A*N K*A*P*L*A*N (1959) and O K*A*P*L*A*N! My K*A*P*L*A*N! (1976), were not as well received.

While at Look, Rosten edited a series of articles that formed the basis of A Guide to the Religions of America (1955), noted for its readability and scholarly accuracy. The Story Behind the Painting (1962), a respected popular art-history book, also grew from a magazine assignment. Rosten enjoyed instant success with The Joys of Yiddish (1968), a comic dictionary of Yiddish words and their many nuances, which he expanded in The Joys of Yinglish (1989). A later collection of humorous tidbits entitled Leo Rosten's Carnival of Wit was published in 1994.