Traveller is a series of related science fiction role-playing games, the first published in 1977 by Game Designers' Workshop and subsequent editions by various companies remaining in print to this day. The game was inspired from such classic science fiction stories as the Dumarest saga series by E. C. Tubb, the Foundation stories of Isaac Asimov, H. Beam Piper's Space Viking, Larry Niven's Known Space, Jerry Pournelle's CoDominium, Poul Anderson's Polesotechnic League and several other works of science fiction literature.

Characters typically journey between various star systems and engage in activities such as exploration, ground and space battles, and interstellar trading. Traveller characters are defined less by the need to increase native skill and ability and more by achievements, discoveries, or obtaining wealth, gadgets, titles and political power.

Originally Traveller was intended to be a system for playing generic space opera-themed science fiction adventures in much the same sense that Dungeons & Dragons was a system intended for generic fantasy adventures. Marc Miller, one of the original designers of the Traveller RPG for Game Designer's Workshop, said that the idea for creating Traveller came about when he said "I want to do Dungeons & Dragons in space.". Most published supplements for Traveller deal in some way with a default setting called the "Third Imperium", (sometimes referred to as the Official Traveller Universe (OTU)), but the main rules are generic enough so that a campaign can be played in any setting the referee (as the game master is referred to) chooses.