Apocalyptic, Holocaust, and Post-Apocalyptic – Stories concerning the end-of-the-world or its aftermath.

Cross-genre – science fiction with one or more other genres sharing focus.

Cyberpunk – Set in a high-tech, often bleak, futuristic universe populated with computers, hackers, computer/human hybrids, and virtual environments.

Biopunk – Focuses on the use of bio-technology and genetic engineering. Similar to Cyberpunk.

Alien Invasion/First Contact – Pretty self-explanatory. This subgenre explores how the human race deals with contact (usually negative) from an alien species. Personally I feel that this covers not just threats from space, but previously unknown terrestrial threats (of an intelligent nature).

Hard Science Fiction – Contains science and technology that is both plausible and central to the plot. An author must generally have a good grasp of the scientific principles involved in order to explain in detail.

Soft/Sociological Scifi – Character driven stories about how technology affects social changes, personal psychology, or people’s interactions with each other. In these stories why society is affected is more important than how the technology works.

Military Science Fiction – Combat in the future with futuristic weapons. Contains the usual military themes of honor, loyalty, sacrifice, etc.

Time Travel – Deals with the issues presented by characters who have the ability to travel in time.

Alternative Universe/Parallel Worlds – Concerns characters traveling to different universes that are similar to, but vary slightly from, our own.

Robot Fiction – deals primarily with the science of robotics and its effects on society.

Space Opera – Usually set in space, these are the “epic” stories involving a large number of characters, multiple story arcs, and large-scale events and wars.