Military
Military science fiction uses interplanetary or interstellar war as a setting and often stresses traditional military attributes. Many times the story is told from the point of view of a soldier or officer. Some examples of military science fiction include:

• Starship Troopers (1959) by Robert Heinlein: A young soldier advances through a futuristic military that uses powered armor to fight a war against insectoid aliens
  
• The Honor Harrington series by David Weber: The series follows an officer in the Royal Manticoran Navy.
  
• Forever War (1975) by Joe Haldeman: A university student is drafted for an interplanetary war. The war last thousands of years from Earth's perspective, but only a few years from the soldier perspective. Soldiers who return to civilian life are hit with culture shock.
  
• Spin State (2003) by Chris Moriarity: Soldiers are wired for enhanced speed and power, their memories backed up on hard drives. Catherine Li is a UN peacekeeper who has spent her life passing for human and thanks to her job, has very few memories that weren’t wiped from her mind. Her ‘official’ memories may not even be true.
  
• The work of John Ringo
  

Apocalypse/ post-apocalypse
This sub genre examines the end of civilization after a world altering disaster, such as nuclear war, natural disaster or alien invasion. Some examples of apocalypse/ post apocalypse science fiction include:

• The Postman (1985) by David Brin: A 'doomwar' survivor is robbed by bandits. While trying to regain his possessions he finds a mail truck of undelivered mail. His story of being sent to establish mail routes brings hope to other survivors.
  
• I Am Legend (1954) by Richard Matheson: A man is the only survivor of a plague that results in vampirism. I am Legend is the basis for the movie "The Omega Man" and a major inspiration for George Romero's "Night of the Living Dead".
  
• Dies the Fire by SM Stirling (2004): A mysterious event causes all electronic devices to stop working and modern humans must learn to live the old ways.
  

Alien Invasion/ Alien Contact
Aliens are common in science fiction. Often, the aliens are technologically superior and have come to colonize or destroy the earth. But other times, aliens are benevolent. Some examples of alien science fiction include:

• War of the Worlds (1898) by HG Wells: The classic story tells of a devastating alien invasion.
  
• The Puppet Masters (1951) by Robert Heinlein: Aliens land on Earth and take over the bodies of humans.
  
• Contact (1985) by Carl Sagan: Scientists looking for signs of extraterrestrial life receive a message telling them how to build a vehicle to travel the Milky Way.
  
• Xenogenesis (1987-89) series (also called Lilith's Brood) by Octavia Butler: And alien race needs to abduct humans to cure their own evolutionary dead end caused by excessive genetic engineering.
  

<===Part One: Hard Scifi vs Soft Scifi
<===Part Two: Technological Scifi
===>Part Four: Alternate History, Time Travel and Humor