Belton, John (October 1, 1995). Movies & Mass Culture. Rutgers Depth of Field. New Brunswick, NJ: Rutgers University Press. p. 85. ISBN0813522285. Retrieved January 1, 2021.
"The Marx Brothers: Passports". THE MARX BROTHERS A DIFFERENT PERSPECTIVE ON THE GREATEST COMEDY TEAM OF THE TWENTIETH CENTURY. Retrieved January 1, 2021.
brightwalldarkroom.com
Osborne, Graham (August 8, 2017). "Humor (Plus) Risk". Bright Wall/Dark Room. Retrieved January 1, 2021.
britannica.com
"Marx Brothers". Britannica. Encyclopedia Britannica. Retrieved December 1, 2020.
McLaughlin, Carrol (Summer 1983). "Harpo Marx"(PDF). American Harp Journal. 9 (1): 51–52. Archived from the original(PDF) on January 21, 2021. Retrieved January 1, 2021.
"Groucho: A Life in Revue". Internet Off-Broadway Database. Lucille Lortel Theatre. Retrieved January 1, 2021.
iymoney.com
"Son of Harpo Speaks". It's Your Money and Your Life Radio Show. Richard J. Muscio. January 2, 2016. Retrieved January 1, 2021.
jewishvirtuallibrary.org
American Jewish Historical Society (October 19, 1999). American Jewish Desk Reference. New York, NY: Random House Reference. pp. 467–468. ISBN0375402438. Retrieved December 1, 2020.
McLaughlin, Carrol (Summer 1983). "Harpo Marx"(PDF). American Harp Journal. 9 (1): 51–52. Archived from the original(PDF) on January 21, 2021. Retrieved January 1, 2021.