Landsraad

The Landsraad is the body that represents all the Great Houses in the Imperium. It is ruled by the High Council and overseen by the Padishah Emperor.
The Landsraad Council meets regularly, and provids a forum within which Great Houses can relate with one another, to either negotiate trade agreements, create alliances or conduct kanly, the formalised processes of vendetta, or feud. It is also supposed to protect the Great Houses from being singled-out by the Imperial House and eliminated by it.
In terms of military strength, all the Great Houses, were they to unite through the Landsraad, would be a match for the Imperial Sardaukar forces.
The Landsraad is governed by the High Council. It presids over issues such as the forms of Kanly, and whether certain Houses should be banished for breach of the Great Convention.
Motions are passed by a vote. Great Houses maintain the "lion's share" of the vote, while the Imperial House also have a powerful vote. Minor Houses have a lesser vote. However, even the Emperor has to answer to the High Council on some issues.