Triplanetary is a science fiction board wargame originally published by Game Designers' Workshop in 1973.

Triplanetary was designed by Marc W. Miller and John Harshman, loosely based on novels and short stories from the Golden Age of Science Fiction, particularly the Future History works of Robert Heinlein.

"[2]: 53  As Miller related, a late-night session of Lensman with Harshman using blank hex-grid battle board combat "inspired the design for Triplanetary, with its image of our solar system and use of vector movement".

[3] In 1976, GDW released Triplanetary Variant V/2, an expansion of the suggested "Prospecting" scenario that was part of the original Errata sheets.

[6] The game was originally packaged in a square cardboard tube, which contained a 16-page book of rules (with four pages of errata and clarifications that included two additional scenarios); a hex map of the inner Solar System; a clear acetate overlay for the map, a grease pencil, a set of cardboard counters representing the various spaceships, and a 6-sided die.

In Issue 4, Scott Rusch gave the original version of Triplanetary a very positive review, saying, "It's quite a flexible game, and it's fun.

"[11] In his 1977 book The Comprehensive Guide to Board Wargaming, Nicholas Palmer thought the game had "a relatively realistic scope [...] the system is not difficult, though it takes a little getting used to."

"[12] In the July 1981 edition of Dragon, Tony Watson welcomed the return of Triplanetary as one of the best SF games on the market.

He admitted that the game wasn't perfect, especially the messy map caused by continuously adding grease pencil trails during a long scenario.

"The designer has apparently decided to sacrifice this bit of realism for the sake of playability, and it seems to make a great deal of sense."

41), William A. Barton reviewed the 1981 edition of Triplanetary, and noted the disappearance of two scenarios from the original list, "Invasion" and "Piracy".

Barton felt the editing of the new rules in was not clean, stating, "GDW should release an errata sheet.