Skaven society is a clan structure, with the four most powerful clans being Clan Moulder, Clan Eshin, Clan Skryre, and Clan Pestilens. The Lords of these clans make up the Skaven ruling council, known as the Thirteen Lords of Decay. There are twelve representatives of the Clans on this council, with the final seat being taken by the Horned Rat himself, the patron god of the Skaven. From here they make plans to spread disease and pestilence across the entire Warhammer World.
Skaven armies are huge seething masses of ratmen, operating in large regiments, led by poweful characters. However, the thing which makes Skaven so interesting is the huge variety of special weaponry which they can use. Designed by the Warlocks of Clan Skryre, war machines such as the giant Doomwheel are used to crush the enemy, and blow them apart with bolts of Warp Lightning. Also, the crazed Poison Wind Globadiers often run alongside regiments of Clanrats, ready to throw thier vile poisons on the enemy once they have begun fighting. Add to this the giant Rat-Ogres, Warpfire throwers, powerful Grey Seers, and many other troops, you have a very entertaining, if unreliable, army.