When a Independant House reaches a certain size, the exact dimensions of which are debatable, they apply to the Kuito who decide whether they have achieved sufficiant size and given enough to the Empire to warrant elevattion to Great House status. The Kuito passes the request on to the Political Council which makes the decision, but if they are denied the House may not re-apply for 100-years. For this reason smaller Houses rarely even petition the Kuito.
Once Great House status is granted they are officially made member fo the Kuito, and as such are allowed their House Crest and Colours to be recorded.
In 329AE there are approximately 150 Great Houses in the Kuito. At the peak there have been as many as 2,000, at the lowest, 15.
Only the leader of the Great Houses listed in the Kuito are permitted to stand for election into the Political Council, and only the leaders of Great Houses can vote for the 12 who will rule the Empire.