Alternative Histories and Parallel Histories
SF in this category presents realities slightly different than our own. An alternate history novel explores a time period in the past that differs from true history. A parallel history novel shows a current reality different from our own because of slightly different events that occurred in the past.

Alternate History and Parallel History examples:
'Darwinia : A Novel of a Very Different Twentieth Century', by Robert Charles Wilson
'The Guns of the South', by Harry Turtledove
'The Eyre Affair', by Jasper Fford
'The Wild Blue and the Gray', by William Sanders

Cyberpunk
This SF subgenre explores the issues of near futures in which science and technology have taken over and created a dismal society. "Bladerunner" and "The Matrix" display this type of SF on the screen. Cyberpunk became well-known in the 1980's and typically has a 1940's-type detective character in a SF setting.

Cyberpunk examples:
'Neuromancer (Remembering Tomorrow)', by William Gibson
'Snow Crash (Bantam Spectra Book)', by Neal Stephenson
'The Shockwave Rider', by John Brunner
'Holy Fire (Bantam Spectra Book)', by Bruce Sterling

Hard Science Fiction
In these SF novels, the emphasis is placed upon science and technology. The "science" in "science fiction" plays a larger role in this subgenre than in the others. The hard sciences include physics, astonomy, chemistry, geology and a few more. The authors of these SF stories have to combine research and knowledge with storytelling--and not sound like a textbook.

Hard Science examples:
'Rendezvous with Rama', by Arthur C. Clarke
'Gateway (Heechee Saga)', by Frederick Pohl
'Ringworld', by Larry Niven
'Red Mars (Mars Trilogy)', by Kim Stanley Robinson

Humorous Science Fiction
Humor and science fiction combine to make satire. SF aficionados enjoy these paradies, but the stories also appeal to a general audience. As a result, these novels are sometimes marketed as mainstream literature.

Humorous Science Fiction examples:
'The Hitchhiker's Guide to the Galaxy', by Douglas Adams
'To Say Nothing of the Dog', by Connie Willis
'Phule's Company (Phule's Company, No 1)', by Robert Asprin

Military Science Fiction
This sub-genre explores the trials soldiers face during war of the future.

Military Science Fiction includes:
'Starship Troopers', by Robert Heinlein
'The Forever War', by Joe Haldeman
'Warlord', by David Drake
'Komarr (Miles Vorkosigan Adventures (Paperback))', by Lois McMaster Bujold

Sociological Science Fiction
Also known as "Soft Science Fiction", this sub-genre deals with worlds facing serious social and moral problems. The sciences of anthropology, sociology and psychology play large roles in these novels.

Sociological Science Fiction examples:
'The Speed of Dark (Ballantine Reader's Circle)' by Elizabeth Moon
'The Left Hand of Darkness (Remembering Tomorrow)', by Ursula K. Le Guin
'A Canticle for Leibowitz (Bantam Spectra Book)', by Walter M. Miller Jr.
'Fahrenheit 451', by Ray Bradbury

Space Opera
This is the SF category into which "Star Wars" falls. The plot is usually an epic story with the "good guys" fighting the "bad guys." "Space Opera" is to SF what "Horse Opera" is to Western novels. The characters are usually making a living in space, such as merchants or law enforcers, and there are some cliches like lazer-type guns, space princesses, and evil monsters with tentacles. These novels are the guilty-pleasures of the SF reader.

Space Opera examples:
'A Fire Upon The Deep (Zones of Thought)', by Vernor Vinge
'Sundiver (The Uplift Saga, Book 1)', by David Brin
'A Princess of Mars (Mars (del Rey Books Numbered))', by Edgar Rice Burroughs
'Singularity Sky', by CharlesStross

Science Fantasy
This sub-genre is a form of space opera in which the science fiction has a few "magical" or "fantastic" elements. The elementcould be a dragon, amystical force, or a special power. Anything can happen in science fantasy and it covers a large part of the SF genre.

Science Fantasy examples:
'The Mote in God's Eye', by Larry Niven and Jerry Pournelle
'Ender's Game (Ender Wiggin Saga)', by Orson Scott Card
'Dragonflight (Dragonriders of Pern Trilogy (Paperback))', by Anne McCaffrey
'Perdido Street Station', by China Mieville

Time Travel
Traveling through time, with all of its paradoxes and twists, plays a large role in the plots of these SF novels.

Time Travel examples:
'The Time Machine (Tor Classics)', by H.G. Wells
'Lest Darkness Fall & Bring the Light', by L. Sprague De Camp
'Timescape', by Gregory Benford
'The Big Time', by Fritz Lieber

Utopias and Dystopias
Utopias are paradise worlds; everything is perfect. Dystopias are warped societies.

Utopia examples:
'Dune (Dune Chronicles, Book 1)', by Frank Herbert
'Foundation (Foundation Novels (Paperback))', by Isaac Asimov
'Childhood's End', by Arthur C. Clarke

Dystopia examples:
'Brave New World', by Aldous Huxley
'1984', by George Orwell
'The Dispossessed', by Ursula K. Le Guin

More sub-sub-genres of SF exist, but these are the main ones. Many more excellent examples could be listed for each kind of SF, but this list should get you started. Of course, most of these books fall into more than one category; most of the authors write for more than one sub-genre. Connie Willis, for example, is listed under the Humorous SF section, but her novel, 'Doomsday Book', is a serious time travel tale that keeps readers on the edge of their seats. Enjoy exploring the different types of Science Fiction novels.