13 titles- Science-Fiction Handbook: The Writing of Imaginative Fiction (New York: Hermitage House, 1953) anonymous, with L Sprague de Camp
- Spirits, Stars and Spells: The Profits and Perils of Magic (New York: Canaveral Press, 1966) with L Sprague de Camp
- 3000 Years of Fantasy and Science Fiction (New York: Lothrop, Lee and Shepard, 1972) with L Sprague de Camp
- Tales Beyond Time, from Fantasy to Science Fiction (New York: Lothrop, Lee and Shepard, 1973) with L Sprague de Camp
- Science-Fiction Handbook, Revised (Philadelphia, Pennsylvania: Owlswick Press, 1975) with L Sprague de Camp
- Creatures of the Cosmos (Philadelphia, Pennsylvania: Westminster Press, 1977)
- Footprints on Sand: A Literary Sampler (Chicago, Illinois: Advent: Publishers, 1981) with L Sprague de Camp
- The Bones of Zora (Huntington Woods, Michigan: Phantasia Press, 1983) with L Sprague de Camp
- Dark Valley Destiny: The Life of Robert E Howard (New York: Bluejay Books, 1983) with L Sprague de Camp and Jane Whittington Griffin
- The Incorporated Knight (West Bloomfield, Michigan: Phantasia Press, 1987) with L Sprague de Camp
- The Stones of Nomuru (Norfolk, Virginia: The Donning Co, 1988) with L Sprague de Camp
- The Pixilated Peeress (New York: Ballantine Books/Del Rey, 1991) with L Sprague de Camp
- The Swords of Zinjaban (New York: Baen Books, 1991) with L Sprague de Camp