Tree houses are buildings constructed among the branches, around or next to the trunk of one or more mature trees, and are raised above the ground. Tree houses can be used for recreation, work space, habitation or as temporary retreats. In some areas the wildlife, climate and illumination on ground level in areas of dense close-canopy forest is not well suited for human habitation, and tree houses are constructed to create improved conditions.
Because they do not require a clearing of a certain area of forest, tree houses are an option for building eco-friendly facilities in remote forest areas. In some parts of the tropics, ordinary houses are built in trees or elevated on stilts to keep the living quarters above hazards at ground level, and to keep the occupants and any stored food out of reach of scavenging animals. The Korowai, a Papuan tribe in the southeast of Irian Jaya, live in tree houses, some nearly 40 metres (130 ft) high, as protection against a tribe of neighbouring head-hunters, the Citak.
The tree house has been central to various environmental protest communities around the world, in a technique known as tree sitting. This method may be used in protests against proposed road building or old growth forestry operations. Tree houses are used as a method of defense from which it is difficult and costly to safely evict the protesters and begin work. Julia Butterfly Hill is a particularly well known tree sitter who occupied a Californian Redwood for 738 days, saving the tree and others in the immediate area. Her accommodation consisted of two 29 square foot platforms 200ft above the ground.
A very small number of planning departments have specific regulations for tree houses, which set out clearly what may be built and where. In some cases tree houses are given exemption from normal building regulations, as they are not considered to be a building in the normal sense of the word. There may be restrictions on height, distance from boundaries and privacy for nearby properties.