Ace Books published 8 Ace doubles between 1952 and 1961 that did not fit the usual genre categories of its 1952 to 1978 Doubles series. All those miscellaneous volumes were published in the famous "dos-à-dos" binding (actually tête-bêche format), whose use continued to 1974.
Ace published science fiction, mysteries, and westerns, as well as books in none of those genres. Collectors of its three main genres have found the Ace doubles an attractive set of books for the unusual appearance of the dos-à-dos format. Eight of the doubles, listed below, do not fit any one of the three genres.
Each listing gives a publication date; in all cases that is year of publication by Ace, with the given catalog number, not the earliest publication date of the contents. 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.