Chestnut is a common name for several species of trees in the genus Castanea (Cas-tá-ne-a) , in the Beech family Fagaceae. Chestnuts are native to warm temperate regions of the Northern Hemisphere. The name also refers to the edible nuts produced by these trees. Most are large trees to 20-40 m tall, but some species are smaller, often shrubby. All are flowering broadleafs with catkins.

The leaves of the American and European chestnut are simple, ovate or lanceolate, 10-30 cm long and 4-10 cm broad, with sharply pointed, widely-spaced teeth, with shallow rounded sinuses between. The flowers are catkins, produced in mid summer; they have a heavy, unpleasant odour (Bean 1970). The fruit is a spiny cupule 5-11 cm diameter, containing one to seven nuts. Chestnut trees thrive on acidic soils, such as soils derived from granite or schist, and do not grow well on alkaline soils such as limestone. When wanting to grow chestnut trees on such soils, the practice was to graft them onto oak rootstocks.

Neither the horse chestnut (family Sapindaceae; also called "buckeye") nor the water chestnut (family Cyperaceae) is closely related to the chestnut, though both are so named for producing similar nuts. The name Castanea comes from an old Latin name for the sweet chestnut.

Interestingly Leo D. Stoller, an American "entrepreneur" copyrighted the word Chestnut. Based in Chicago, Stoller claimed rights to a large inventory of trademarks. He engaged in the assertive enforcement of those trademark rights in the United States, threatening infringement action against people and companies who attempt to infringe these marks. These include STEALTH, SENTRA, DARK STAR and CHESTNUT. He allegedly filed large numbers of enforcement actions, but eventually was made bankrupt. On August 8, 2007, the bankruptcy court approved an auction and sale under which Stoller's trademark assets were transferred to the Society for the Prevention of Trademark Abuse, LLC.