The original Eon edition of Cosmic Encounter was released in 1977. It included 15 aliens and supported up to four players. After a total of 9 expansions, the number of aliens had increased to 75 and players to six.
Fifteen aliens were included with this edition:
A total of nine expansion sets were released, which were numbered rather than named:
- Expansion 1 (1977): 10 new aliens and orange (silver in early print runs) components for a 5th player
- Expansion 2 (1977): 10 new aliens and purple (gold in early print runs) components for a 6th player
- Expansion 3 (1978): 15 new aliens and new cards for the deck
- Expansion 4 (1979): Flares for all currently-existing aliens
- Expansion 5 (1980): Moons
- Expansion 6 (1981): Lucre and 10 new aliens, many of which made use of Lucre
- Expansion 7 (1981): 14 new aliens
- Expansion 8 (1982): Flares for all aliens from E6, E7 and the upcoming E9, and new cards for the deck, including the new Kickers
- Expansion 9 (1983): 1 new alien and stickers for two new gameplay variants
With all expansions included, this edition contained 75 aliens.