Allies are an important part of Cosmic Encounter and can often make the difference in battles. After the offense launches ships, both main players may invite other players to join them. A player who has been invited to ally may accept or decline; if a player accepts, he or she places 1-4 ships in the hyperspace gate (if allying with the offense) or next to the targeted planet (if allying with the defense).
If the offense wins, all offensive allies land their ships on the targeted planet along with the offense, granting each of them a new colony (or reinforcing an existing colony if the player already has one there).
If the defense wins, each defensive ally receives rewards equal to the number of ships he or she had in the encounter.
If the main players end up attempting to make a deal, all allies return their ships to their colonies. Allies do not participate in deals and get nothing from them.