Ace Books is a publisher of science fiction (SF) and fantasy books founded in New York City in 1952 by Aaron A. Wyn. It began as a genre publisher of mysteries and westerns, and soon branched out into other genres, publishing its first science fiction title in 1953. This was successful, and science fiction titles outnumbered both mysteries and westerns within a few years. Other genres also made an appearance, including nonfiction, gothic novels, media tie-in novelizations, and romances. Ace became known for the tête-bêche binding format used for many of its early books, although it did not originate the format. Most of the early titles were published in this "Ace Double" format, and Ace continued to issue books in varied genres, bound tête-bêche, until 1973.

Ballantine Books is a major American book publisher that is a subsidiary of German media conglomerate Bertelsmann. Ballantine was founded in 1952 by Ian Ballantine with his wife, Betty Ballantine. Ballantine was acquired by Random House in 1973, which in turn was acquired by Bertelsmann in 1998 and remains part of that company.