Daniel Martin Klein (born 1939 in Wilmington, Delaware) is an American writer of fiction, non-fiction, and humor. His most notable work is Plato and a Platypus Walk Into a Bar co-written with Thomas Cathcart. It was a New York Times bestseller and is translated into 26 languages.

Klein went to school at Harvard College where he received a B.A. in philosophy. After a brief career in television comedy, he began writing books, ranging from thrillers and mysteries to humorous books about philosophy. He lives in Great Barrington, Massachusetts, and is married to Freke Vuijst, American correspondent for the Dutch newsweekly, 'Vrij Nederland'.