There are twelve different races, with each race posessing a distinct set of racial traits. Each race has at least one faction - some have more, each bearing a close resemblance to the main strain of their race but often posessing slightly different traits or victory conditions.
In large custom games every race can spawn several AI controlled empires although the sub-factions seem to be unique and appear exactly once.
While some races seem overpowered when compared to others, these advantages in racial traits are balanced out by the method used to aquire victory points. Not every race has to win by killing everything in sight.