Sometimes called speculative fiction, a genre of writing that is concerned with a world removed in some fundamental way from our own, whether in time, attitude or knowledge. It encompasses many sub-genres such as Hard Science Fiction, where the implications of possible scientific advance are explored, Space Opera, which usually includes scantily clad alien babes and Bug Eyed Monsters, and Utopian or Dystopian visions of the future. Depending on whom you ask, the line between Science Fiction and fantasy tends to blur, and Alternate History, which explores the result of some change in the past, doesn't fit comfortably under either term, but is often discussed with both.
Science Fiction explores what-ifs. Like what if there were Food Factories In Orbit?
Sci Fi is my favourite genre of fiction. I first starting reading Sci Fi at the age of sixteen when I started work in a supermarket. I often spent my lunches reading old Sci Fi books purchased from the local market. -- Chris Watson
This guy is my husband, and I tell you, he reads too many damn Sci Fi books! -- Ann Watson
"Science Fiction is something that could happen - but usually you wouldn't want it to. Fantasy is something that couldn't happen - though often you only wish it could."
Arthur Cee Clarke in the Introduction to "The Collected Stories of Arthur C. Clarke"
(Yes, that's just the sort of thing one would expect Clarke to say. It's subtly wrong, in a nasty way, but it's close enough for most purposes.)
Film:
Plan Nine From Outer Space (Cheap SciFi), Gattaca, all the Star Wars movies.
'It Camefrom Outer Space', 'Forbidden Planet', 'The Day The Earth Stood Still', et al.
Book:
most of Phil Dick's work, of which some is genuinely dreadful and some is great philosophical literature masquerading as junk. Please comment on which is which in the Phil Dick page
Book Of The New Sun by Gene Wolfe - Some of the best science fiction I have come across.
1984(Nineteen Eighty Four) by George Orwell
Magazines
Locus Magazine - What's New BEST for Keeping Up www.locusmag.com 
Analog Magazine Science Fiction and Fact - www.analogsf.com
Asimov's Science Fiction - www.sfsite.com
Fantasy & Science Fiction - www.fsfmag.com
Great Science Fiction Authors: people.qualcomm.com
Ezines
Infinite Matrix - www.infinitematrix.net
Strange Horizons - www.strangehorizons.com
Speculon - www.speculon.com (defunct)
Event Horizon - www.eventhorizon.com (defunct)
Key Outside Science Fiction Web Pages
Science Fiction, fantasy, and horror from Infinity Plus www.users.zetnet.co.uk
Sci Fi.Com www.scifi.com - Science Fiction TV channel plus more
SFF Net www.sff.net
The SF Site: The Best in Science Fiction and Fantasy www.sfsite.com
Sci-Fi Wiki: Woytex Wiki www.pobratyn.com (since May 2003, defunct!)
Science Fiction Writers of America: www.sfwa.org
the list seems to be coming along nicely, but we could use a concise definition. Maybe:
Fiction that is as based on technology or science extrapolations or presuming some key change in knowledge compared to now. Hard Science Fiction requires that it be strictly self-consistent and believable [meaning no "magic" may assist the special effects].
Certainly Science Fiction, like science itself, is based on the assumption that the universe is knowable even though the greatest part of it may be unknown and may be destined to remain mysterious for the life of any of us, or, indeed, the life of all of us, by which I mean the human species. The knowable universe has no room for the supernatural, or those experiences that by their very nature can never be "known." To bring experiences of the transcendent or the ineffable into the natural world is to destroy one or the other.
Are you saying here that the science-fiction worldview has no place for the divine, or the mysterious, or anything that cannot be cleanly classified as some sort of scientific phenomena? I can think of a couple of Science Fiction authors who might argue against such a distinction, including Alan Moore, William Burroughs, and Kurt Vonnegut. -- francis
I agree with Frances. Whoever, wrote the above, why do you think that with Science Fiction? Many writers factor the unknown or some sense of the mysterious with Science Fiction.
-- sg
I think the key word in the original text was "knowable" rather than known. Also, I'm not sure that William Burroughs can be classed as Science Fiction within the definition we're discussing. And Kurt Vonnegut is even more difficult - I'll grant you something like "Galapagos" is SF (Darwin again...), but Slaughterhouse Five, say, is much less easy to pidgeonhole.
Agreed. I'm not sure I would class William Burroughs or Kurt Vonnegut as Science Fiction either. -- sg
Kurt Vonnegut has written about: new molecules (Ice Nine in "Cat's Cradle"), evolution ("Galapagos"), the mechanization of all work ("Player Piano"). William Burroughs, in "Naked Lunch", writes about topics such as cloning, psychic mind control, and (if I remember correctly) genetic engineering. I know that most Science Fiction fans don't consider the two authors part of the genre, but I've never understood concretely why. Can someone offer a useful definition of the genre that excludes the two?
As for the question of "knowability", I don't understand what use there is in a distinction between the "known" and the "knowable". If that's simply the distinction between what we rationally know today, and we can rationally know in the future, that doesn't really address the issue of knowledge that is transcendent, or mystical, or instinctive. -- francis
You raise good points. I have to think about it.
There is a distinction clear and concise between the "known" and the "knowable". If you start with a philosophical "I think therefore I know" and proceed along the lines of how one comes to "know". Knowledge is proliferated, the "known" is what is in ones "mind set". The "knowable" is that external to that mind set which can become a part of that set. In a secular sense, a library is full of "knowable" knowledge, a university is an agent of change in the conversion of what is "knowable" into what is "known". If by transcendent, mystical, instinctive you mean thoughts not extracted from the secular "knowable" mentioned, you are talking about ideas, which seem to come from nowhere, when in fact they do come from somewhere, even if that somewhere is the subconscious, or a spiritual awareness. Ideas also come to be known, but must be proliferated through oral or written communication to be "knowable".
Also, consider that heavily-explained magic can still fit into a SF paradigm. Consider the treatment of magic in some Larry Niven stories, such as "Burning City" or the short story "What Good is a Glass Dagger?" Magic exists, but it involves a natural resource, "manna", which is channeled by a mage and is limited in quantity. Although it's a supernatural phenomenon, it's explainable, quantified, and subject to its own "natural" laws. It may be outside of our everyday experience, but since it can be understood, I think it still qualifies as SF, or perhaps "Science Fantasy" (see below). -- Joseph Riesen
My understanding was that Vonnegut's resistance to being labeled SF was a marketing ploy, which he has softened on considerably now that he is safely famous. I'll never forget a friend of mine, as I was trying to explain that not all SF sucked, who said, "But Vonnegut can't be science fiction, Vonnegut is good." She never was too fond of logic (and at least admitted it). My personal definition of SF is that genre which attempts to disprove all definitions hazarded for it.
-- John Abbe
Mary Wollstonecraft Shelley provided as good a definition of SF as any in her preface to Franken Stein:
The event on which this fiction is founded has been supposed, by Dr. Darwin, and some of the physiological writers of Germany, as not of impossible occurrence. I shall not be supposed as according the remotest degree of serious faith to such an imagination; yet, in assuming it as the basis of a work of fancy, I have not considered myself as merely weaving a series of supernatural terrors. The event on which the interest of the story depends is exempt from the disadvantages of a mere tale of spectres or enchantment. It was recommended by the novelty of the situations which it develops; and, however impossible as a physical fact, affords a point of view to the imagination for the delineating of human passions more comprehensive and commanding than any which the ordinary relations of existing events can yield.
To see the original essay "The Worldview of Science Fiction" by James Gunn (with the proper attributions), see web.archive.org . -- Kyle Brown
See also:
Science Fiction Golden Age Science Fiction British Science Fiction Fandom Science Fiction New Wave Sci Fi Authors Science Fiction Wiki Forum in Public Wiki Forums Wanted Deviant Sci Fi
Some of the Great Books Lists recommend specific Science Fiction books - see Science Fiction Books To Consider.
Can one distinguish between Science Fiction and Science Fantasy? Does anyone even have a good definition? I see the two of them lumped together often, and every now and then a mellow argument breaks out between various people I know. I have yet to see a good, solid definition that makes any sense...
Science fiction differs from science fantasy in that science fiction must obey the Laws of Nature. (That's one view.)
I think 'Science Fantasy' is sort of an arbitrary assertion, when you want to describe a novel with a bit of science that also contains fantasy elements. For instance, consider a lot of work by Roger Zelazny, such as Creatures of Light and Darkness, or Changeling. Or, for that matter, where do Piers Anthony's 'Blue Adept' novels fit in? There's science... but there's fantasy. As such, I think 'Science Fantasy' is sort of a warning label to explain that there's real magic or something similar going on, not just more "easily explained" processes like psionics. Generally speaking, when supernatural elements become involved that aren't explainable (and are more than just philosophical) in the context of the book, that's where fantasy leaks in. Just my two cents. :)
One of the problems in defining science fiction is that there are at least three broad definitions that I'm aware of:
There's the more-or-less literal definition: Science Fiction is fiction about science - "hard" SF - fiction where the story and/or setting relies on scientific or technological advances and explores the consequences of them - often characterised by the author showing their working (in the text, in appendices, or in notes published separately).
Then there's the intuitive definition: Science Fiction is fiction that includes enough of the marker tropes of science fiction - if it's set in space, involves people traveling by some kind of hyperdrive, and has some kind of aliens present, then it's science fiction by this definition, even if the actual science is completely lacking - Star Wars (particularly the original trilogy) falls under this definition.
Thirdly there's the commercial definition: Science Fiction is fiction that's marketed primarily toward science fiction fans - it's the stuff that ends up shelved under "science fiction" in your local library. Barring freak occurrences, everything that comes under this definition will also fit at least one of the other definitions - it's the anomalies that don't fit this definition that are most interesting. Take, for example, a story about a man with a genetic condition that means he travels in time unaided: Poul Anderson's novel There Will Be Time (shelved under SF) or Audrey Niffenegger's The Time Traveller's Wife (shelved under General Fiction) - the latter meets all the criteria for fairly hard SF - it is the postulation of a single new technology/discovery (the genetic condition that allows him to travel through time) and the exploration of the logical consequences of it - but it's marketed, not to SF fandom, but to the generic reading public...
TechLand's 5 most underrated sci-fi flicks: techland.time.com
See original on c2.com