SUBGENRES

ALIENS ON EARTH: they came from outer space

ALTERNATE WORLDS: history might have happened differently

ANTIGRAVITY: what goes up may not come down

BAMBI'S CHILDREN: animals who speak, think, or act human

BEAM ME UP: matter transmission, techno-teleportation

BEYOND THE FIELDS WE KNOW: magical world unconnected to ours

CITIES OF THE FUTURE: bigger, better, and more astonishing urban visions

CLONES: stories of genetic engineering, especially of people

CYBER PUNK: gritty near-future tales of hackers and cyberspace

DYSTOPIA: really, really bad futures (opposite of "Utopia")

EXTRA-SENSORY PERCEPTION: telepathy, psi, other paths to the mind

FEMINIST: science fiction and fantasy of, by, or for women

HARD SCIENCE FICTION: based on real science & engineering

HEROIC FANTASY: also known as "Swords & Sorcery"

HORROR: that old black magic, the really scary stuff

IMMORTALITY: Those who live forever, or try to

INVISIBILITY: Mostly about people who can't be seen

LOST LANDS/LOST RACE: neoprimitive place/people discovered

MYTHOLOGY: Mythology and Science Fiction or Fantasy about Religion

POLITICS: science fiction about social and political concerns

SEX: science fiction authors who also write erotica

SPACE OPERA: battles between planets and stars

SPACE TRAVEL: rockets to asteroids, moons, planets, stars

SUPERMEN: extra powers make characters more than human

THEOLOGY: Science Fiction or Fantasy about Religion

THERE AND BACK AGAIN: leave our world for a more magical one

TIME TRAVEL: time machines, travel to the past or the future

TV and MOVIE: books spun-off from television series or sci-fi films

UNDER THE SEA: submarines, undersea cities, underwater living

UNICORNS IN THE GARDEN: magic events within our mundane world

UTOPIA: Fictional and Nonfictional glimpses of an ideal future

WORLD COMES TO AN END: no more civilization, or people, or worse...

YOU CAN TELL A BOOK BY ITS COVER: science fiction, fantasy, horror

As listed by Ultimate SF Web Guide

For a discussion of each subgenre, see the above website.