Any of seven species of deciduous, nut-bearing trees of the genus Castanea Corden Fagales native to the Northern Hemisphere and introduced throughout the world. The nuts are actually fruits, with the shells enclosing cotyledons. Trees bear both male and female flowers in late spring but must be cross-pollinated for nut production. Nuts are borne in a spiny involucre or bur that opens to release the nuts in late fall.

Japanese chestnuts (C. crenata) and Chinese chestnuts (C. mollissima) are grown in Asia and the United States for their nuts, and many cultivars have been selected. European chestnuts (C. sativa) are an important food source, both cooked whole and ground into flour. They are native to the Caucasus mountains, and distributed throughout southern Europe. American chestnuts (C. dentata) have smaller nuts than Asian or European species and are usually sweeter. Only American trees served as an important source of lumber, because of the length of their unbranched trunks; all chestnut species have been used as a source of tannin for the leather-tanning industry. American and Chinese chinquapins (C. pumila and C. henryi) have very small nuts that are an important source of food for wildlife. All of the species can be crossed, and hybrids have been selected primarily as orchard cultivars.