There are four Clans in the forest, and one "lost" Clan. The forest Clans are ThunderClan, RiverClan, WindClan, and ShadowClan. The "lost" Clan is SkyClan. Almost every book is based mainly in ThunderClan, a strong and loyal Clan residing in a deciduous forest. RiverClan lives on an island near a river. These cats have adapted to swim well. ShadowClan lives in a dark and gloomy pine forest, and are rumored to be an untrustworthy and sly Clan. WindClan is in an open moor. These cats have adapted to be very swift due to the daily task of catching rabbits. Now, the "forgotten" Clan, SkyClan, is a Clan made up of former kittypets and loners. They hunt mostly in trees, and use a special type of attack in which they drop from trees to surprise opponents.
StarClan is a group of cats composed of the deceased Clan cats that remained faithful. Some cats, however, turn against the Clans and are permitted to the Dark Forest, a horrid place that is set on the destruction of StarClan and the four Clans.
In the recent books, SkyClan was re-implemented to the lake and now lives beside the other warrior Clans.