Master of Orion (abbreviated as MoO) is a turn-based, 4X science fiction strategy game in which the player leads one of ten races to dominate the galaxy through a combination of diplomacy and conquest while developing technology, exploring and colonizing star systems.

Sometimes described as a scifi-themed spin-off of classic Civilization, the game has proven to be quite enduring, becoming a cult classic in its niche of sci-fi-themed 4X strategy games. It has received several direct sequels, and additionally, a number of other games published since have been described as inspired by it, with reviewers and players divided on whether any has succeeded at recapturing the feeling and gameplay of the original.

The game was released in 1993 by MicroProse on the MS-DOS operating system. It was ported to the Mac OS in 1995 by Take-Two Interactive and distributed by GameTek. It is the first in its franchise, and the rights are held by Wargaming.