44 titles- There's Adventure in Electronics (Chicago, Illinois: Popular Mechanics Press, 1957)
- There's Adventure in Chemistry (Chicago, Illinois: Popular Mechanics Press, 1957)
- There's Adventure in Atomic Energy (Chicago, Illinois: Popular Mechanics Press, 1957)
- There's Adventure in Rockets (Chicago, Illinois: Popular Mechanics Press, 1958)
- There's Adventure in Astronautics (New York: Hawthorne Books/A Popular Mechanics Book, 1961)
- Frankenstein (Mankato, Minnesota: Crestwood House, 1977)
- A Gazeteer of the Hyborian World of Conan (Fax Collector's Editions, 1977)
- Godzilla (Mankato, Minnesota: Crestwood House, 1977)
- Dracula (Mankato, Minnesota: Crestwood House, 1977)
- King Kong (Mankato, Minnesota: Creative Educational Society, 1977)
- Mad Scientists (Mankato, Minnesota: Crestwood House, 1977)
- The Wolf Man (Mankato, Minnesota: Crestwood House, 1977)
- The Many-Colored Land (Boston, Massachusetts: Houghton Mifflin Company, 1981)
- The Mummy (Mankato, Minnesota: Crestwood House, 1981)
- Frankenstein Meets Wolfman: Adapted from the Screenplay "Frankenstein Meets the Wolfman" by Curt Siodmak (Mankato, Minnesota: Crestwood House, 1981) with Howard Schroeder and Curt Siodmak
- The Golden Torc (Boston, Massachusetts: Houghton Mifflin Company, 1982)
- Brede's Tale (Mercer Island, Washington: Starmont House, 1982)
- The Many-Colored Land & The Golden Torc (Garden City, New York: Nelson Doubleday, 1982)
- Creature from the Black Lagoon (Mankato, Minnesota: Crestwood House, 1982)
- The Blob (Mankato, Minnesota: Crestwood House, 1982)
- The Deadly Mantis (Mankato, Minnesota: Crestwood House, 1982)
- It Came from Outer Space (Mankato, Minnesota: Crestwood House, 1982)
- The Nonborn King (Boston, Massachusetts: Houghton Mifflin Company, 1983)
- The Adversary (Boston, Massachusetts: Houghton Mifflin Company, 1984)
- The Nonborn King & The Adversary (Garden City, New York: Nelson Doubleday, 1984)
- The Pliocene Companion (Boston, Massachusetts: Houghton Mifflin Company, 1984)
- A Pliocene Companion: A Guide to the Saga of Pliocene Exile (New York: Ballantine Books/Del Rey, 1985)
- Intervention (Boston, Massachusetts: Houghton Mifflin Company, 1987)
- The Surveillance (New York: Ballantine Books/Del Rey, 1988)
- Metaconcert (New York: Ballantine Books/Del Rey, 1989)
- Black Trillium (New York: Doubleday Foundation, 1990) with Marion Zimmer Bradley and Andre Norton
- Blood Trillium (New York: Bantam Spectra, 1992)
- Jack the Bodiless (New York: Alfred A Knopf, 1992)
- Golden Trillium (New York: Bantam Spectra, 1993) by Andre Norton
- Diamond Mask (New York: Alfred A Knopf, 1994)
- Lady of the Trillium (New York: Bantam Spectra, 1995) by Marion Zimmer Bradley
- Sky Trillium (New York: Ballantine Books/Del Rey, 1996)
- Magnificat (New York: Alfred A Knopf, 1996)
- Perseus Spur: An Adventure of the Rampart Worlds (London: HarperCollins/Voyager, 1998)
- Orion Arm: An Adventure of the Rampart Worlds (London: HarperCollins/Voyager, 1999)
- Sagittarius Whorl: An Adventure of the Rampart Worlds (New York: Ballantine Books/Del Rey, 2001)
- Conqueror's Moon (London: HarperCollins/Voyager, 2003)
- Ironcrown Moon (London: HarperCollins/Voyager, 2004)
- Sorcerer's Moon (New York: Ace Books, 2006)