Science fiction, as I like to define it, is fiction based on the imagined exploration of scientific possibility. The distinction from fantasy—or from other sorts of fantasy—lies in the word possibility.

Science Fiction is the fiction of ideas. Ideas excite me, and as soon as I get excited, the adrenaline gets going and the next thing I know I’m borrowing energy from the ideas themselves. Science fiction is any idea that occurs in the head and doesn’t exist yet, but soon will, and will change everything for everybody, and nothing will ever be the same again. As soon as you have an idea that changes some small part of the world you are writing science fiction. It is always the art of the possible, never the impossible.

Science fiction is a literature of possibilities.

Science fiction may be defined as that branch of literature which deals with the response of human beings to advances in science and technology. Actual change in science and technology, occurring quickly enough and striking deeply enough to affect a human being in the course of his normal lifetime, is a phenomenon peculiar to the world only since the Industrial Revolution ... The first well-known writer who responded to this new factor in human affairs by dealing regularly with science fiction, by studying the effect of additional scientific advance upon mankind ... was Jules Verne. In the English language, the early master was H. G. Wells. Between them, they laid the foundation for every theme upon which science fiction writers have been ringing variations ever since.

Science Fiction is a combination of entertainment and education. Out of any genre, Science Fiction is the one genre that allows us to go deeper into topics that are difficult to talk about.

Science fiction is a literature that belongs to all humankind.

A science fiction story is a story built around human beings, with a human problem and a human solution, which would not have happened at all without its scientific content.

Science Fiction is a collection of guerrilla bands each challenging the rights of the others to belong to the centrality. The band most challenged by the others is ‘high fantasy’, sometimes called ‘Sword and Sorcery’. There is a lot of stylized sneering at ‘S and S’.

(Why science fiction?) Science fiction is the only genre that not only allows you to disregard everything that we're taught is realistic and practical, but actually demands that you do. So it allows us to move beyond the bounds of what is realistic and what is real, into the realm of the imagination, That is actually something that organizers do every single day.

Science fiction … means what we point to when we say it.

I have come to prefer something looser, a rough sort of definition which says simply that science fiction attempts to portray that which does not exist, a speculative reality, but endeavors to explore the consequences of such a speculation in a rigorous, systematic, and scientifically plausible way.

Science fiction gives you the information you need to figure out what’s happening in our world.

Much blood has also been spilled on the carpet in attempts to distinguish between science fiction and fantasy. I have suggested an operational definition: 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 that it could.

Science fiction, thus considered, is not a mere pocket in the varicolored vest of modern writing; it is a new kind of fiction, the beginnings of a long-delayed revolution in letters consequent upon the revolutions that the last two hundred years have witnessed in science, industry, and politics. By this I do not at all mean that it is the only possible literature of the present time, just that it is the type most peculiar to it, most indicative of its larger intellectual trends.