Ellery Queen is both a fictional character and a pseudonym used by two American cousins from Brooklyn, New York: Daniel 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. During the 1930s and much of the 1940s, that detective-hero was possibly the best known American fictional detective. 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, generally considered as one of the most influential English crime fiction magazines of the last sixty-five years.