If we described the Traveller universe in a few short sentences (to capture the feel of the game and the flavor of society), here's what we would say…

• · The fastest you can get information somewhere is in a ship.
  
• · A ship takes at least a week to get somewhere.
  
• · The Imperium is a government of men, not laws, and it rules space. Planets rule themselves.
  
• · The lifeblood of the Imperium is commerce. Don't get in the way of the Imperium's lifeblood.
  
• · There is no Prime Directive. If you want to sell guns to the natives, go ahead. Check first to see if they have anything you want.
  

• 
  Classic Traveller.
  The original Traveller, and the one players continue to play and enjoy. Classic Traveller is set in the Golden Age of the Third Imperium.

• 
  MegaTraveller.
  Traveller's second edition, introducing the task system and extensive rules revisions. MegaTraveller covers the era of the Rebellion and breakup of the Third Imperium.

• 
  Traveller: The New Era.
  Traveller's third edition, carrying play forward into the aftermath of the Rebellion. The rules implement a D20 system compatible with Twilight: 2000 version 2.2.

• 
  Marc Miller's Traveller.
  Traveller's fourth edition, published by Imperium Games. Play is set in the early days of the Third Imperium.

• 
  GURPS Traveller.
  The Steve Jackson Games transformation of Traveller into the Generic Universal Role Playing System. GURPS Traveller is set in the Golden Age in an alternate branch universe in which Emperor Strephon was not assassinated.

• 
  T20 Traveller.
  The Quiklinks transformation of Traveller to the D20 system. T20 is set in the Gateway sector.