Science-fiction, or "scf-fi" is a type of speculative fiction. It is based upon real or imagined scientific theories or advanced technology. Authors explore the alternative possibilities of currently held laws of nature, making it a ‘literature of ideas’. Scientific discoveries, space travel, alien creatures, life on other planets, environmental changes or different dimensions often form part of the plot of SF stories.

Hard SF:

Hard science fiction, or "hard SF", is characterized by rigorous attention to accurate detail in quantitative sciences, especially physics, astrophysics, and chemistry, or on accurately depicting worlds that more advanced technology may make possible.

• Asimov, Isaac
• Baxter, Stephen
• Bear, Greg
• Benford, Gregory
• Clement, Hal
• Egan, Greg
• Hamilton, Peter F.
• Heinlein, Robert
• Landis, Geoffrey A.
• Niven, Larry
• Reynolds, Alastair
• Rucker, Rudy
• Sawyer, Robert J.
• Vinge, Vernor

Soft or Social SF:

Soft, or Social SF is the other end of the spectrum from Hard SF. Its focus is on the social sciences, anthropology, sociology, psychology, philosophy or political science. It is more concerned with character, society, or other speculative ideas and themes that are not centrally tied to the physical sciences. This type of SF is more character driven, and while technology may play a role, the emphasis is not so much on how that technologu works, but how it affects individuals or social groups.

• Bradbury, Ray
• Bujold, Lois McMaster
• Card, Orson Scott
• Dick, Philip K.
• Herbert, Frank
• Kress, Nancy
• Le Guin, Ursula K.
• Modessit, L.E., Jr.
• Vinge, Joan
• Zindell, David

Cyberpunk:

A subgenre that emerged in the early 1980s, in which the time frame is usually near-future and the settings are often dystopian (characterized by misery), high-tech and peopled with computer/human hybrids.
Common themes in Cyberpunk include advances in information technology and especially the Internet, artificial intelligence and prosthetics and post-democratic societal control where corporations have more influence than governments.

• Bester, Alfred
• Brunner, John
• Cadigan, Pat
• Gibson, William
• Jeter, K.W.
• Lem, Stanislaw
• Rucker, Rudy
• Shirley, John
• Sterling, Bruce
• Stephenson, Neal

Time Travel:

Stories about traveling in time, either back
into the past or forward into the future, (and
sometimes involve traveling in space as well),
often with the use of a time machine.

• Baker, Kage
• Fforde, Jasper
• Gabaldon, Diana
• Heinlein, Robert A.
• Robinson, Spider
• Simak, Clifford D.
• Wells, H.G.
• Willis, Connie

Alien Encounters:

Stories dealing with first contact with an alien race and/or alien invasion. First contact explores the initial meeting between humans and aliens, who are sometimes benign beings wanting to share secrets of advanced technology, while in alien invasion tales, the beings use their technological superiority in an attempt to enslave or eradicate human life on earth.

• Brin, David
• Card, Orson Scott
• Haldeman, Joe W.
• Heinlein, Robert A.
• Kress, Nancy
• Macleod, Ken
• Niven, Larry
• Sawyer, Robert J.
• Silverberg, Robert
• Simak, Clifford D.
• Wells, H.G.
• Wilson, Robert Charles

Robots/Androids:

Stories about man-made organic beings. Androids
in particular are made to look human, and given artificial intelligence, often making them both
mentally and physically superior to humans.
Most fiction explores the discrepancy between
their human appearance and nonhuman matter, or their quest to become human or rebel against
human oppressors. The stories are, essentially, about what it means to be human.

• Adams, Douglas
• Asimov, Isaac
• Bradbury, Ray
• Dick, Philip K.
• Pratchett, Terry
• Simmons, Dan

Apocalyptic/Dying Earth:

Apocalyptic stories focus on the end of the world due to a host of causes – comets and asteroids, nuclear holocaust, plague, etc. Often, a group of survivors endure the resulting hardships in an attempt to maintain their survival and continue on. Dying earth tales depict a slower end and could be due to any cause, including natural.

• Adams, Robert
• Brooks, Terry
• Dick, Philip K.
• Harrison, M. John
• King, Stephen
• McCarthy, Cormac
• Miller, Walter M.
• Shute, Nevil
• Stewart, George R.
• Vance, Jack