Ellery Queen is both a fictional character and a pseudonym used by two American cousins from Brooklyn, New York: Daniel (David) Nathan, alias Frederic Dannay (October 20, 1905–September 3, 1982) and Manford (Emanuel) Lepofsky, alias Manfred Bennington Lee (January 11, 1905–April 3, 1971), to write detective fiction.

In a successful series of novels that covered 42 years, Ellery Queen served as both author's name and that of the detective-hero. Movies, radio shows, and television shows have been based on their works. The two, particularly Dannay, were also responsible for co-founding and directing Ellery Queen's Mystery Magazine, considered one of the most influential English crime fiction magazines of the last sixty-five years. They were also prominent historians in the field, editing numerous collections and anthologies of short stories such as The Misadventures of Sherlock Holmes. The cousins also wrote four novels about a detective named Drury Lane using the pseudonym Barnaby Ross, and allowed the Ellery Queen name to be used as a house name for a number of novels written by other authors.

Under their collective pseudonym, the cousins were given the Grand Master Award for achievements in the field of the mystery story by the Mystery Writers of America in 1961.