Collectors of these genres have found the Ace doubles an attractive set of books to collect, because of the unusual appearance of the tête-bêche format.
All volumes containing two SF works, in the entire 1952 to 1978 series, are listed below, with the late change in format noted.
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.
Another Ace SF double(G-723-Andre Norton-Star Hunter/Voodoo Planet) was published in 1968 as a traditional reprint in the second G series (begun in 1964).
The remaining novels do not have complete date information, so they are sorted in numerical order of the serial number.