The Eldar's society model early in the First Age was a monarchy where supreme power lay on a High King of the Eldar, Ingwë. However, from the beginning of the Ages of the Stars the Eldar live in a meritocracy; that is, power lies on individuals based on their achievements in various fields.
The Supreme Command is at the top of the chain. Under this Supreme Commander are the High Commanders of Arda and Kúma. Downwards on the chain the command branches to cover more specific areas.
Star Command is composed of all kinds of Eldar; however, the internal divisions tend to prefer one of the three races for historical reasons:
This does not mean that each division is exclusive for a certain race; rather, it means few Eldar are skilled enough in areas they don't normally excel at. Cases exist where Eldar could be accepted into any area. Such is the case of most descendants of Ingwë and Círdan.
Due to the fact that the first Eldar to be in space were only Vanyar for many years, they are the dominant race in terms of population.