Aztec series
- Aztec (1980) : A story of the Aztec empire just before and during the arrival of the Spanish.
- Aztec Autumn (1998), a story of the Aztecs following the Spanish conquest.
Three further books in the series (
Aztec Blood, 2002;
Aztec Rage, 2006;
Aztec Fire, 2008) were written by Robert Gleason, Jennings' former editor, and Junius Podrug, working from notes left by Jennings.
Novels
- The Terrible Teague Bunch (1975) : about a gang of Texas outlaws at the tail end of the Old West
- Sow the Seeds of Hemp (1976) : about a fire-breathing preacher in Mississippi
- The Journeyer (1984) : An account of the travels of Marco Polo to the Far East.
- Spangle (1987) : A chronicle of the lives of circus entertainers. Also released in paperback, split into a trilogy: The Road Show, The Center Ring and The Grand Promenade.
- The Lively Lives of Crispin Mobey (by 'Gabriel Quyth') (1988) : "A novel of the hilarious chronicle of the exploits of an all-too-zealous missionary." Mostly assembled from a series of short stories published under Jennings's real name in The Magazine of Fantasy and Science Fiction 1972-1979.
- Raptor (1992) : Thorn, a hermaphrodite, and his/her adventures in a post-Roman world.
For young adults
- March of the Robots: From The Manikins Of Antiquity To The Space Robots Of Tomorrow (1962)
- The Movie Book (1963)
- Parades!: Celebrations and circuses on the march (1966)
- The Teenager's Realistic Guide to Astrology (1971)
- The Shrinking Outdoors (1972)
- The Killer Storms: Hurricanes, Typhoons, and Tornadoes (1974)
- Black Magic, White Magic (1975)
- March of the Heroes: The folk hero through the ages (1975)
- March of the Gods (1976)
- The Rope in the Jungle (a novel) (1976)
- March of the Demons (1977)
For preschool readers
Nonfiction
- Personalities of Language (1965)
- World of Words: The Personalities of Language (1967)
- The Treasure of the Superstition Mountains (1973)