He wrote about 50 novels, 150 novelettes, and around 100 short stories.
His most famous series was the "Telzey Amberdon" adventures series featuring Telzey Amberdon, an interstellar adventurer.
Other series included:
- "Elusion", where the protagonist is the pilot of a spaceship with the ability to change its appearance.
- "The Game Players of Zan", set on the planet Zan where games of strategy and conflict determine social status and power.
- "Simak-land", stories set in worlds similar to those of Clifford D. Simak.
- "The Void Trilogy":
-1. "The Void Beyond" (1968)
-2. "The Transcended Void" (1969)
-3. "Inalienable Void" (1971)
- "The Zorome", a series of novellas and novels written between 1968 and 1972, about human colonists from Earth who settle on a planet inhabited by giant reptiles.
He also wrote the "Venus War" shared-world series with the following entries:
- "Venus War" (1968)
- "The Masters of Venus War" (1969)
- "Venus Triumphant" (1970)
He also published stand-alone novels such as "The Mind Master of Mars" (1963) and "Dark of day" (1969).