Ace Books was founded in 1953 by A. A. Wyn, and is the oldest continuously operating science fiction publisher in the United States. With Donald A. Wollheim as editor, it issued some of the most outstanding science fiction writers of the 1950s and 1960s, including Samuel R. Delany, Philip K. Dick, Ursula K. Le Guin, and Robert Silverberg. Ace was known for marketing innovations such as the Ace Doubles, which contained two short novels bound back to back, and for the critically acclaimed Ace Specials edited by Terry Carr. In 1972, Wollheim left the company, and it was later acquired by Grosset & Dunlap. Under Publisher Tom Doherty, Ace produced books in all genres, though science fiction remained a specialty. In 1982, Grosset & Dunlap was acquired by The Putnam Berkley Group and Ace soon became Berkley’s science fiction imprint.