Many early Ace books contained two short novels (often heavily edited to keep within the size limitations) bound back to back, but upside down with their own covers — this is known as the Ace Double format. Through the 50s and 60s Ace and Ballantine Books were the dominant SF publishers.
Donald A. Wollheim was unhappy at Avon Books landed a job as editor with Wyn at Ace. And then in the mid 60s, science fiction author Terry Carr joined Ace and started the Ace Science Fiction Specials series of more sophisticated SF, including authors like Ursula K. Le Guin. Carr and Wollheim co-edited an annual Year's Best Science Fiction anthology series; and Carr also edited Universe, an important series of original anthologies.
In 1965, Wollheim arranged for Ace to publish The Lord of the Rings by J. R. R. Tolkien. He believd that Tolkien's copyright was invalid because the Houghton Mifflin edition had been bound using pages printed in Great Britain for the hardcover edition there. By US copyright law the text was public domain in the US. Ace Books published the first paperback edition of Tolkien's work, with cover art by Jack Gaughan. This did not sit well with fans and Ballantine published an revised and authorized edition with a special statement by Tolkien himself asking readers to avoid the Ace edition.
After A. A. Wyn's death, Ace Books was a division of Charter and then was acquired by Grosset & Dunlap, and then by by G. P. Putnam's Sons. Later Penguin acquired the Putnam Berkley, and retained Ace as their sf imprint.
Carr later returned to Ace Books as a freelance editor and launched a new and very successful series of Ace Specials devoted entirely to first novels. It included Kim Stanley Robinson's The Wild Shore, Lucius Shepard's Green Eyes, William Gibson's Neuromancer, and Michael Swanwick's In the Drift.
Other prominent sf publishing figures who have worked at Ace include Tom Doherty, who left to start Tor Books, and Jim Baen, who left to work at Tor and later founded Baen Books. Other notables who have worked at Ace include Frederik Pohl, Terri Windling, Susan Allison Beth Meacham and Ginjer Buchanan.