Its theme is to build galactic civilizations via game cards that represent worlds or technical and social developments.

At the start of each round, all players simultaneously and secretly choose one of five phases: Explore, Develop, Settle, Consume, or Produce.

Unusually among card games, cards discarded due to the hand limit or when paying a cost are placed face-down (in a "messy" pile to distinguish them from the draw deck), concealing information that could be used to deduce upcoming draws.

Lehmann, Race's designer, developed his own card game version of Puerto Rico at the request of the publisher.

Later, Lehmann used those ideas to create a different game, one of space exploration, settlement, and conquest rather than development in the colonial Caribbean.

[9] During playtesting, plans were made for two expansions[8][10] to add more variety to gameplay, shore up certain strategies, and to accommodate more players.

These expansions thematically focus on a struggle for galactic control between the militarily powerful Imperium and a Rebel uprising.

The first expansion adds components for a fifth player, additional cards, goals (opportunities to gain extra victory points chosen at random at game start), and rules and components for solo play (against a "robot" player).

Each round the player(s) with the most prestige earn an additional victory point and possibly a card.

Additionally, a new "once-per-game" action is introduced that allows the user to search the deck for a card meeting a specific stated requirement, or to enhance the bonus the user earns in a round (at the cost of one prestige).

[19] The set further extends takeover options: the Interstellar Casus Belli development can allow attacks against anyone, and the Imperium Planet Buster can destroy enemy worlds outright.

Players can earn bonuses by contributing to the war effort, but the game can also end in two new ways: repulsing the Xeno threat or losing to the invaders.