The fungi are among the least known and least appreciated components of forest ecosystems. The vast majority of the species present are microfungi and cannot be easily observed directly in nature, thus usually escaping our attention. However, fungi are absolutely essential for the functioning of the forest ecosystem. Saprotrophic fungi play an important role in regulating natural processes, including the decomposition of dead plant material. All trees are dependent upon the mycorrhizal associations they establish with fungi, while parasitic and pathogenic fungi reduce the fitness of their plant hosts, including trees, sometimes resulting in the death of the host. Macrofungi produce fruiting bodies that are visible to the naked eye, and these fruiting bodies are fed upon by a wide variety of animals, and those of some species are collected and eaten by humans. Although most fruiting bodies are ephemeral and do not persist more than a few days, many are conspicuous enough to be easily noticed. The ecological roles and different types of fungi associated with the forests of the Appalachians and Ozarks are discussed in this chapter.