From 1949 to 1953, Clement's first three novels were two-, three-, and four-part Astounding serials under Campbell: Needle (Doubleday, 1950), Iceworld (Gnome Press, 1953), and Mission of Gravity (1954), his best-known novel, published by Doubleday's Science Fiction Book Club (established 1953). The latter novel features a land and sea expedition across the superjovian planet Mesklin to recover a stranded scientific probe. The natives of Mesklin are centipede-like intelligent beings about 50 centimeters long. Various episodes hinge on the fact that Mesklin's fast rotational speed causes it to be considerably deformed from the spherical, with effective surface gravity that varies from approximately 3 gn at the equator to approximately 700 gn at the poles.
Clement's article "Whirligig World" describes his approach to writing a science fiction story:
Writing a science fiction story is fun, not work. ...the fun...lies in treating the whole thing as a game.... [T]he rules must be quite simple. They are; for the reader of a science-fiction story, they consist of finding as many as possible of the author's statements or implications which conflict with the facts as science currently understands them. For the author, the rule is to make as few such slips as he possibly can... Certain exceptions are made [e.g., to allow travel faster than the speed of light], but fair play demands that all such matters be mentioned as early as possible in the story...
Clement was a frequent guest at science fiction conventions, especially in the eastern United States, where he usually presented talks and slide shows about writing and astronomy.
Clement has been honored several times for his cumulative contributions including 1998 Hall of Fame induction, when Clement and Frederik Pohl were the fifth and sixth living persons[a] honored, and the 1999 SFWA Grand Master Award.
For the 1945 short story "Uncommon Sense" he received a 50-year Retro Hugo Award at the 1996 World Science Fiction Convention. Mission of Gravity, first published as a serial during 1953, was named best foreign novel by the Spanish Science Fiction Association in 1994 and it was a finalist for a 50-year Retro Hugo Award in 2004.
The Hal Clement Award for Young Adults for Excellence in Children's Science Fiction Literature is presented in his memory at Worldcon each year.
Planets created by Clement typically feature unique astronomical or physical aspects. They include:
Abyormen – A planet circling a dwarf star (Theer), which in turn circles a blue giant. This produces a hot and a cold season, each of 65 years' duration. The native intelligent life forms undergo a seasonal mass death. From Cycle of Fire.
Dhrawn – A high-gravity world settled by Mesklinites in Star Light.
Habranha - A planet that is tidally locked with its sun, such that the dark side is a mix of solid CO2, solid methane, and ice, and the sunlit side completely ocean, in Fossil.
Hekla – An ice-age planet in "Cold Front" (a short story in Astounding July 1946).
Kaihapa – An uninhabited ocean planet, twin of Kainui, in Noise.
Mesklin — A planet with ultra-high gravity (up to 700 g) in Mission of Gravity. Clement later corrected his model of Mesklin and determined that the maximum surface gravity would be "only 250 gravities".
Sarr – An extremely hot planet with an atmosphere of gaseous sulfur, and little liquid (the natives occasionally need to drink a bit of molten copper chloride), in Iceworld
Enigma 88 - A small planet near η Carinae in Still River. The interior of the object is honeycombed with caves, due to evaporation of accreted ice-rich planetoids. Unusually for Clement, Enigma's structure is not fully consistent with the laws of physics.
Impediment (aug 1942). Novelette. Published in Astounding. Collected in Natives of Space, The Best of Hal Clement and The Essential Hal Clement Volume 2.
Avenue of Escape (nov 1942). Published in Astounding's series Probability Zero. Collected in The Essential Hal Clement Volume 2.
"Attitude" (September 1943). Novella. Published in Astounding. Collected in The Essential Hal Clement Volume 2 and Travellers of Space (1951).
Technical Error" (January 1944). Novelette. Published in Astounding. Collected in Natives of Space, The Best of Hal Clement and The Essential Hal Clement Volume 2.
"Trojan Fall" (June 1944). Short story. Published in Astounding. Collected in Small Changes.
"Uncommon Sense" (September 1945). His most famous short story. Part of the Laird Cunningham Series. Hugo Award for Best Short Story of 1945. Published in Astounding. Collected in Small Changes, The Best of Hal Clement, Intuit, The Essential Hal Clement Volume 2, The Old Masters (1970), Out of This World 10 (1973) and Nebula Awards Showcase 2000 (2000).
"The Mechanic" (September 1966). Novelette. Published in Analog. Collected in Small Changes, The Essential Hal Clement Volume 2 and Analog: Writers’ Choice, Volume II (1984).
"Bulge" (September 1968). Novelette. Published in If. Collected in Small Changes and The Essential Hal Clement Volume 2.
'"Planetfall" (1972). Original version of "Planet for Plunder" (1957). Published in Strange Tomorrows (1972). Collected in The Essential Hal Clement Volume 2.
"Lecture Demonstration" (1973). Short story from the Mesklin Series (of Mission of Gravity fame). Published in the book Astounding (1973). Collected in The Essential Hal Clement Volume 3, Heavy Planet and Mission of Gravity (1978).
"Mistaken for Granted" (January/February 1974). Novella. Published in Worlds of If. Collected in The Best of Hal Clement.
"The Logical Life" (1974). Second short story in the Laird Cunningham Series. Published in Stellar #1 (1974). Collected in Intuit and The Essential Hal Clement Volume 2.
"Stuck with It" (1976). Novelette innthe Laird Cunningham Series. Published in Stellar #2 (1976). Collected in The Best of Hal Clement, Intuit and The Essential Hal Clement Volume 2].
"Longline" (1976). Novelette. Published in Faster than Light (1976). Collected in The Essential Hal Clement Volume 2.
"Seasoning" (September/October 1978). Novelette set in Harlan Ellison's Medea world. Not included in any of Hal Clement's compilations. Published in IASFM. Collected in Medea: Harlan's World (1985) and Aliens and UFO's (1993).
"Status Symbol" (1987). Novelette, the last story in the Laird Cunningham Series. Published in Intuit. Collected in The Essential Hal Clement Volume 2.
Probability Zero! (nov 1942). Published jointly with Malcolm Jameson, Harry Warner Jr., Dennis Tucker and P. Schuyler Miller in Astounding. About Probability Zero, Harry Harrison said in the John Campbell Memorial Anthology:
"In the early 1940s, in Astounding, there was a small department called Probability Zero! that ran short-short stories. Or items. Or lies. Things. These things were usually funny and always impossible - echoing the description of the title."
Whirligig World (jun 1953). About how to write science fiction, and specifically, about how he wrote Mission of Gravity. Published in Astounding. Collected in The Essential Hal Clement Volume 3, Heavy Planet and Mission of Gravity (1978).
Some Notes on Xi Bootis. Published by Advent Publishers.
Gravity insufficient (nov 1961). Published in Analog Science Fact.
^""Henry Clement Stubbs"". Archived from the original on July 20, 2008. Retrieved 2006-05-30.CS1 maint: BOT: original-url status unknown (link). Rosetta Books (rosettabooks.com). Archived 2008-07-20. Retrieved 2013-03-23.
^Hal Clement at the Internet Speculative Fiction Database (ISFDB). Retrieved 2013-04-04. Select a title to see its linked publication history and general information. Select a particular edition (title) for more data at that level, such as a front cover image or linked contents.