Ace published science fiction, mysteries, and westerns, as well as books not in any of these genres.
Collectors of these genres have found the Ace doubles an attractive set of books to collect, because of the unusual appearance of the dos-a-dos format.
The list given here gives a date of publication; in all cases this refers to the date of publication by Ace, and not the date of original publication of the novels.
For more information about the history of these titles, see Ace Books, which includes a discussion of the serial numbering conventions used and an explanation of the letter-code system.
The following reference has not been seen but covers the Ace Doubles: