Florence Mendheim (January 13, 1899 – August 1984) was a New York Public Library branch librarian notable for her undercover surveillance of American Nazi groups in the pre-World War II 1930s. She was the daughter of German-Jewish immigrants and an observant Jew who practiced kosher dietary laws. Her personal papers, including documentation of her spy activities, are housed in the archives of the Leo Baeck Institute in New York.