Science fiction is a genre of fiction. It differs from fantasy in that, within the context of the story, its imaginary elements are largely possible within scientifically-established or scientifically-postulated laws of nature (though some elements in a story might still be pure imaginative speculation).
- Science fiction is the search for a definition of man and his status in the universe which will stand in our advanced but confused state of knowledge (science), and is characteristically cast in the Gothic or post-Gothic mould.
- Brian Aldiss, Billion Year Spree: The True History of Science Fiction (1973), Ch. 1: "The Origins of the Species"
- Individual science fiction stories may seem as trivial as ever to the blinder critics and philosophers of today — but the core of science fiction, its essence, the concept around which it revolves, has become crucial to our salvation if we are to be saved at all.
- Isaac Asimov, in "My Own View" in The Encyclopedia of Science Fiction (1978) edited by Robert Holdstock; later published in Asimov on Science Fiction (1981)
- The hardest theme in science fiction is that of the alien. The simplest solution of all is in fact quite profound — that the real difficulty lies not in understanding what is alien, but in understanding what is self. We are all aliens to each other, all different and divided. We are even aliens to ourselves at different stages of our lives. Do any of us remember precisely what it was like to be a baby?
- Greg Bear, "Introduction to 'Plague of Conscience' ", The Collected Stories of Greg Bear" (2002)
- Fantasies are things that can't happen, and science fiction is about things that can happen.
- Ray Bradbury 
- Science-fiction works hand-in-glove with the universe.
- Ray Bradbury, "Introduction" in The Circus of Dr. Lao and Other Improbable Stories (1956)
- Science fiction is the most important literature in the history of the world, because it's the history of ideas, the history of our civilization birthing itself. ...Science fiction is central to everything we've ever done, and people who make fun of science fiction writers don't know what they're talking about.
- Ray Bradbury, Brown Daily Herald, March 24, 1995
- People who love science fiction really do love sex.
- I hate the whole ubermensch, superman temptation that pervades science fiction. I believe no protagonist should be so competent, so awe-inspiring, that a committee of 20 really hard-working, intelligent people couldn't do the same thing.
- Not only is every sci fi innovation kept secret, so that its flaws won't be uncovered and dealt with ahead of time, but the public seldom is invited to share in the New Thing. Or, if they do partake, they are portrayed using it as stupidly as possible, as in the flick Surrogates, where the brilliant invention of remote robotic surrogacy is only used to look good. Talk about a jaundiced view of your fellow citizens.
- David Brin 
- No less a critic than C. S. Lewis has described the ravenous addiction that these magazines inspired; the same phenomenon has led me to call science fiction the only genuine consciousness-expanding drug.
- Arthur C. Clarke, "Of Sand and Stars", 1983
- Nothing is deader than yesterday's science-fiction.
- Arthur C. Clarke, The Sands of Mars, 1951.
- SF has never really aimed to tell us when we might reach other planets, or develop new technologies, or meet aliens. SF speculates about why we might want to do these things, and how their consequences might affect our lives and our planet.
- John Clute, Science Fiction: The Illustrated Encyclopedia (1995)
- I do watch a lot of television science fiction, and it is a particularly sexless world. With a lot of the material from America, I think gay, lesbian and bisexual characters are massively underrepresented, especially in science fiction, and I'm just not prepared to put up with that. It's a very macho, testosterone-driven genre on the whole, very much written by straight men. I think Torchwood possibly has television's first bisexual male hero, with a very fluid sexuality for the rest of the cast as well. We're a beacon in the darkness.
- Russel T. Davies "Parallel universe". The Age (Melbourne, Australia). 14 June 2007. Retrieved 27 June 2007.
- Science fiction is, after all, the art of extrapolation.
- "There, Master Niketas," Baudolino said, "when I was not prey to the temptations of this world, I devoted my nights to imagining other worlds. ... There is nothing better than imagining other worlds," he said, "to forget the painful one we live in. At least so I thought then. I hadn't yet realized that, imagining other worlds, you end up changing this one."
- Umberto Eco, Baudolino (2000), p. 99.
- I think that science fiction, even the corniest of it, even the most outlandish of it, no matter how badly it's written, has a distinct therapeutic value because all of it has as its primary postulate that the world does change.
- Robert A. Heinlein, "The Discovery of the Future," Guest of Honor Speech, 3rd World Science Fiction Convention, Denver, Colorado (4 July 1941)
- Science-fiction is a literary province I used to visit fairly often; if I now visit it seldom, that is not because my taste has improved but because the province has changed, being now covered with new building estates, in a style I don't care for. But in the good old days I noticed that whenever critics said anything about it, they betrayed great ignorance. They talked as if it were a homogeneous genre. But it is not, in the literary sense, a genre at all. There is nothing common to all who write it except the use of a particular 'machine'. Some of the writers are of the family of Jules Verne and are primarily interested in technology. Some use the machine simply for literary fantasy and produce what is essentially Märchen or myth. A great many use it for satire; nearly all the most pungent American criticism of the American way of life takes this form, and would at once be denounced as un-American if it ventured into any other. And finally, there is the great mass of hacks who merely 'cashed in' on the boom in science-fiction and used remote planets or even galaxies as the backcloth for spy-stories or love-stories which might as well or better have been located in Whitechapel or the Bronx. And as the stories differ in kind, so of course do their readers. You can, if you wish, class all science-fiction together; but it is about as perceptive as classing the works of Ballantyne, Conrad and W. W. Jacobs together as 'the sea-story' and then criticising that.
- C. S. Lewis, An Experiment in Criticism (1961), XI: "The Experiment"
- It is absurd to condemn them [science fiction stories] because they do not often display any deep or sensitive characterization. They oughtn't to. … Every good writer knows that the more unusual the scenes and events of his story are, the slighter, more ordinary, the more typical his persons should be. Hence Gulliver is a commonplace little man and Alice is a commonplace little girl. If they had been more remarkable they would have wrecked their books. The Ancient Mariner himself is a very ordinary man. To tell how odd things struck odd people is to have an oddity too much; he who is to see strange sights must not himself be strange.
- C. S. Lewis, "On Science Fiction", 24 November 1955 talk to the Cambridge University English Club on; published posthumously in Of Other Worlds: Essays and Stories (1966)
- I like to present my characters—whether they are in the past or in the future—with interesting moral choices, and it seems to me that science-fiction writers are, or should be, the prophets and moralists of today. I am fairly well up on the biological sciences, but I am deeply uninterested in gadgets. A writer's job is to write about people with sympathy and insight.
- Naomi Mitchison, in Anthony Wolk, "Challenge the Boundaries: An Overview of Science Fiction and Fantasy," The English Journal 79 (1990), p. 27.
- Brian Rollins says: You're one of the few sci-fi writers in Hollywood to use religion in your shows. What kind of resistance/acceptance do you see from industry insiders and fans?
- Moore: I was amazed that I didn’t get a lot of resistance from the industry. For whatever reason, SCI FI Channel and Universal just let me run with it on Battlestar. They didn’t have problems with it. They had other problems, but they didn’t have any problems with the religious stuff in the show. And the fans, it was an interesting reaction. There’s a surprising core of fandom that just hates any kind of religion in their science fiction. They really don’t want to mix these things together. I’m not quite clear what that’s about and why they’re so opposed to mixing these things. It becomes a very purist argument. People will say, “If there’s any kind of religion in it, it’s not science fiction anymore.” Well, I don’t really buy that. People believe in religions and there are weird, mysterious things that happen in the universe. Why not play with that, too? Why isn’t that just as valid as everything else that’s part of the human condition, which is theoretically what sci-fi is supposed to be exploring.
- Ronald D. Moore 
- Sci-fi can be succinctly defined as speculation, whether based on established scientific facts or on logical pseudo-facts consistent with the framework of the fiction in question, involving smelly green pimply aliens furiously raping or eating, or both, beautiful naked bare-breasted chicks, covering them in slime, red, oozing, living slime, dribbling from every horrific orifice, squeezing out between bulbous pulpy lips onto the sensuous velvety skin of the writhing sweating slave-girls, their bodies cut and bruised by knotted whips brandished by giant blond vast-biceped androids called Simon, and written in the Gothic mode.
- Peter Nicholls, True Rat 7 (1976)
- In schools, for example, there are courses in the criticism of literature, art criticism, and so forth. The arts are supposed to be 'not real.' It is quite safe, therefore, to criticize them in that regard -- to see how a story or a painting is constructed, or more importantly, to critically analyze the structure of ideas, themes, or beliefs that appear, say, in the poem or work of fiction. When children are taught science, there is no criticism allowed. They are told, 'This is how things are.' Science's reasons are given as the only true statements about reality, with which no student is expected to quarrel. Any strong intellectual explorations or counter versions of reality have appeared in science fiction, for example. Here scientists, many being science-fiction buffs, can channel their own intellectual questioning into a safe form. 'This is, after all, merely imaginative and not to be taken seriously.'
- Jane Roberts, in The God of Jane: A Psychic Manifesto, p. 145-146
- Science fiction rarely is about scientists doing real science, in its slowness, its vagueness, the sort of tedious quality of getting out there and digging amongst rocks and then trying to convince people that what you're seeing justifies the conclusions you're making. The whole process of science is wildly under-represented in science fiction because it's not easy to write about. There are many facets of science that are almost exactly opposite of dramatic narrative. It's slow, tedious, inconclusive, it's hard to tell good guys from bad guys — it's everything that a normal hour of Star Trek is not.
- It is said that science fiction and fantasy are two different things. Science fiction is the improbable made possible, and fantasy is the impossible made probable.
- Remember that Jules Verne was a sort of Shakespeare of science fiction, and we would feel derelict if we did not give his stories in our columns.
- There is no such thing as science fiction, there is only science eventuality.
- Science fiction is a very big canvas for a film maker to work on because if you are doing a drama, society imposes its rues on you and you have to live by those guidelines; more or less. But in science fiction you get to make up the rules of the world you create.
- The "hard" science-fiction writers are the ones who try to write specific stories about all that technology may do for us. More and more, these writers felt an opaque wall across the future. Once, they could put such fantasies millions of years in the future. Now they saw that their most diligent extrapolations resulted in the unknowable … soon.
- Vernor Vinge, "The Coming Technological Singularity" (1993)
- I have been a soreheaded occupant of a file drawer labeled "Science Fiction" ever since, and I would like out, particularly since so many serious critics regularly mistake the drawer for a urinal.
- Kurt Vonnegut, The New York Times Book Review, 5 September 1965; reprinted in Wampeters, Foma & Granfalloons (1974)
- We hope it will not be long before we may have other works of Science-Fiction [like Richard Henry Horne’s ‘‘The Poor Artist’’], as we believe such books likely to fulfil a good purpose, and create an interest, where, unhappily, science alone might fail. [Thomas] Campbell says, that ‘‘Fiction in Poetry is not the reverse of truth, but her soft and enchanting resemblance.’’ Now this applies especially to Science-Fiction, in which the revealed truths of Science may be given, interwoven with a pleasing story which may itself be poetical and true—thus circulating a knowledge of the Poetry of Science, clothed in a garb of the Poetry of life.
- Westfahl, Gary. Science Fiction Quotations. Yale University Press. 2005.