Aging of wood begins with the cutting of a tree. The subsequent changes of the wood substance proceed very slowly and depend on environmental conditions. In a hot, dry desert climate wooden objects and cellulose textiles are preserved for several millenia, whereas their degradation is accelerated by conditions which favor the attack of microorganisms. Two conditions under which aging processes take place can be distinguished: a) aerobic conditions as prevailing in wooden buildings, sculptures etc.; b) anaerobic conditions valid for wooden items buried in the ground or submerged in water such as foundation pillars, ships etc. Submersion and underground embedding initiate the very slow process of fossilization in which the cell wall substance is transformed into highly condensed compounds (coalification) or is substituted by minerals (silicification). The various wood components are subjected to different kinds of degradation and conversion. The polysaccharides disappear with aging and seem to be more sensitive than lignin. Although more resistant, the lignin is converted chemically and its structure differs increasingly from its original state. Even extractives may survive millions of years.