Ace Books is the oldest continuously operating science fiction imprint in the United States. Ace's marketing innovations included the famous Ace Doubles and the Ace Specials (edited by Terry Carr).
Ace Books was acquired in 1972 by Grosset & Dunlap, who were in turn acquired by G. P. Putnam's Sons. The resulting monster also owns the Berkely imprint, which among others had published the Dune series.