We may categorize science fantasy in a number of ways, including dying earth, planetary romance, science fantasy otherworlds, space opera, sword and planet, magic science and other subgenres. These will be explained below.
Jack Vance's Dying Earth stories are sometimes classed as science fantasy because the cosmology used is not compatible with that conventionally accepted by science fiction. Other stories in the Dying Earth subgenre such as M. John Harrison's Viriconium novels or Gene Wolfe's Book of the New Sun are usually classed as science fantasy.
The planetary romance, a story set primarily or wholly on a single planet and illustrating its scenery, native peoples (if any) and cultures, offers considerable scope for science fantasy, in the sense of fantasy rationalized by reference to science-fictional conventions.
David Lindsay's A Voyage to Arcturus, published in 1920 is one of the earliest examples of the type, although it differs from most of them in not assuming a science-fictional background of interplanetary or interstellar travel; it is rather a philosophical romance, which uses an alien planet as a background for exploring philosophical themes. C.S. Lewis' Out of the Silent Planet (1938) is an example of the same type of story, though in its case the preoccupations are theological. In both cases the magical elements are barely rationalized, and in Lewis' case stand in stark contrast to the pseudo-scientific machinery that frames the story.
C. L. Moore's Northwest Smith stories fall squarely into the fantasy/horror camp, but utilize a space opera-like frame and various pseudo-scientific rationalization: god or monster as powerful alien for instance.
Some of Leigh Brackett's stories set on Mars and Venus might be regarded as science fantasy, especially those which occur in distant and barbarous parts of the planets, such as People of the Talisman and The Moon that Vanished. Other stories set on the same worlds contain far more science fictional tropes. All of Brackett's stories imply that a rational, scientific explanation for such things as mind-transmission and the ability to create visible illusions is available somewhere, but the explanations are generally assumed rather than attempted.
Frank Herbert's Dune novels are also classed by some as science fantasy, probably because his Arrakis dispenses with many (but not all) of the technological ornaments that conventionally mark a story as "science fiction"; however, his scientifically impossible concepts (like prescience and genetic memory) were staples in mainstream science fiction for many years.
Anne McCaffrey's Pern novels and Marion Zimmer Bradley's Darkover novels are more obvious examples of science fantasy, the former largely because of its choice of the fantasy icon of the "dragon" at the center of the stories, the latter because a form of rationalized magic is a dominant theme. Both share the concept of long-ago lost Earth expeditions that had peopled their respective planets, and over time had regressed to a quasi-medieval state of life.
Some examples of this type of science fantasy deliberately blur the already vague distinction between science fictional paranormal powers and magic; for instance, Poul Anderson's The Queen of Air and Darkness, in which aliens use psionic powers of illusion to imitate earthly myths of fairies -- who are themselves traditionally regarded as magical illusionists.
Some science fantasies use fantasy worlds with the thinnest veneer of science fictional trappings, only distinguishable with difficulty from standard fantasy. An early example of this type is Eric Rucker Eddison's The Worm Ouroboros, nominally set on the planet Mercury, but a Mercury that is indistinguishable in any way from a fantasy Earth.
In Andre Norton's Witch World series, the fantasy world is excused as a parallel universe. There are a few inessential science fictional elements in the earlier stories of this series, which are absent from the later novels.
Terry Brooks' Shannara books represent the fantasy world as the far future of a lost technological civilization (thus sharing some features with the Dying Earth subgenre).
Space opera is not normally thought of as science fantasy, but some examples of space opera invoke vaguely explained, or completely unexplained paranormal powers which approximate magic closely enough for some to regard them as part of the genre. These include E. E. Smith's Lensman series, and George Lucas' Star Wars franchise. Magic plays a major role in Outlaw Star anime series.
Sword and planet
Many works by Edgar Rice Burroughs fall into this category, as well as those of his imitators such as Otis Adelbert Kline, Kenneth Bulmer, Lin Carter, and John Norman. They are largely classed as "science fantasy" because of the presence of swords and, usually, an archaic aristocratic social system; Burroughs' own novels are, however, skeptical in spirit and almost free of any non-rationalized "fantastic" element.
A "magic science" story is a story where magic has replaced or become synonymous with technology. An excellent example would be the magitechnology of the Tales of Symphonia game, as well as the Eberron Campaign Setting for the Dungeons & Dragons role-playing game or the Warhammer 40,000 campaign setting. These stories usually combine archaic elements such as swords and other low-tech weaponry with high-tech elements such as flying vehicles or power generators. The Final Fantasy series can also be considered in the genre of magic science, as there are many advances in technology (i.e. hi-tech airships, advanced armour and weapon technology, enormous technological cities) as well as the use of magic. Yet another Magic Science series is Incarnations of Immortality by Piers Anthony. The Incarnations of Immortality takes place in a reality where magic and science co-exist. In addition, many classical personalities (such as Death, Fate, Time and others) are anthropomorphised and function as major characters.
Science fantasy is sometimes used to refer to a fantasy story in which the fantastic elements are presented as compatible with real-world science, in contrast to fantasies in which the fantastic only needs to have its own internal logic. Classic examples are Poul Anderson's Three Hearts and Three Lions, in which petrification means danger because turning carbon to silicon results in a radioactive isotope, and his Operation Chaos, where werewolves and other lycanthrope are the same size in human and animal form, owing to conservation of mass.
An example of science fantasy in television is the cartoon Visionaries: Knights of the Magical Light, which combined alien fiction, sword and sorcery, magic, technology and the superhero genre - all of them rolled into one coherent vision. Another example is the worlds depicted in the Masters of the Universe franchise.
Science Fantasy is also a popular subject for role-playing games, of both pen-and-paper and computer varieties. Examples include the Rifts and Fading Suns and Shadowrun and Dragonstar role-playing games, a number of Final fantasy games, and the Warhammer 40,000 wargame.