APA (7th ed.) Citation

Marx, G. (1967). The Groucho letters: Letters from and to Groucho Marx. Simon and Schuster.

Chicago Style (17th ed.) Citation

Marx, Groucho. The Groucho Letters: Letters from and to Groucho Marx. New York: Simon and Schuster, 1967.

MLA (9th ed.) Citation

Marx, Groucho. The Groucho Letters: Letters from and to Groucho Marx. Simon and Schuster, 1967.