Empire is a computer game written for the PLATO system in 1973. It is significant for being quite probably the first networked multiplayer arena shooter-style game. It may also be the first networked multiplayer action game (although Maze War is another possibility for this distinction).

Although PLATO terminals had touch panels, they did not have mice, and all control in the game is via typing. Commands involving directions to change course and fire weapons are entered as degree headings, with 0 being to the right, 90 up, 180 left, and 270 down. The "arrow" keys, clustered around "s", could also be used (e.g. "qw" being the same as 113 degrees). PLATO terminals had 512 by 512 pixel monochrome vector CRT display screens, and could use downloadable character sets to display graphics.

The object of the game is to conquer the galaxy. This galaxy contains 25 planets and 4 races. The races were the Federation, Romulans, Orions, and (originally) Klingons. The fourth race was changed to Kazari, just prior to publication because the game authors were worried about copyright infringement. In 1991, the fourth race name was changed back to Klingon on the NovaNET system, but remained Kazari on the CDC systems.

Each team is given three adjacent planets as their home system. Each home system is located towards one corner of the map, which was many screens in size, and thus has two other teams relatively nearby. There are two neutral worlds between each team and its two neighbors, and five more neutral worlds in the middle of the galaxy. Each planet given to a team contains 50 armies at the start of the game, while the neutral planets start off with 25 self-ruled armies.

Up to 30 players could be in the game at once, with no more than 15 players on a team. Each player is given a starship to pilot. Players dogfight each other, destroy enemy armies by bombing them, beam up friendly armies to transport them, and beam down armies to take over planets. The ships of each race have slightly different capabilities; Orion ships have the weakest weapons but are fast, Roms have the strongest weapons, but are the slowest, and Fed and Kazari ships have medium speed and strength. (In the VAX Conquest variant, which features engine and weapons temperature statistics, Federation ships have the highest overall speed; Klingon weapons do the most damage; Orions can "cruise" at a faster speed than others without engine overheat; and Romulans can fire weapons more often without weapon systems overheating.)

Ships have two kinds of weapons: phasers and photon torpedoes. Phasers fire in a cone shape and do damage immediately, while torpedoes take some time to reach their target and can be dodged. Torpedoes can also be detonated before they strike. When a player is killed, they resurrect in a new ship in their home system, or in any home system that has been conquered by their team.

Although an action game, Empire can be slow to play, and moves have to be carefully and yet quickly considered. Flying from a team's home space to engage the enemy could take one to two minutes, and bombing a planet with fifty armies could take five to ten minutes. A game might take many hours, or even days, as players come and go. Yet, in intense dogfighting conditions, players have been known to type as quickly as 20 keys per second (as fast as the system would take them).

Original PLATO terminals were connected to the host system with a 1200 baud connection, and the host computers were quite slow by current standards. Since an update of the screen could take one to two seconds with a lot of ships and torpedoes on the screen, players were allowed to decide when their screen updated, but could not delay this action more than 10 seconds, or execute more than a certain number of commands before an update was forced. The position of each ship was updated only when its player updated his screen, which permitted ships to discontinuously hop or "hyperjump". Conversely, torpedo locations updated whenever any player in the game updated their screen, so their movements were effectively continuous.