* Children of the Apocalypse (1959)
* The Unconquered (1961)
* The Star Lords (1964)
* The Black Death (1966)
* Legion of the Damned (1967)
* The Time Machine (1970)
* The First Men (1973)
* The Final War (1975)
* The Dragon Riders (1977)
* The Last Battle (1979)
Non-Fiction:
* How to Write Science Fiction (1965)
* The Science of Science Fiction (1966)
* The History of Science Fiction (1968)
* The Future of Science Fiction (1970)
* The World of Science Fiction (1972)