Beech (Fagus) is a genus of deciduous trees in the family Fagaceae, native to temperate Eurasia and North America. There are 13 accepted species in two distinct subgenera, Engleriana and Fagus. The subgenus Engleriana is found only in East Asia, distinctive for its low branches, often made up of several major trunks with yellowish bark. The better known Fagus subgenus beeches are native to Europe and North America. They are high-branching trees with tall, stout trunks and smooth silver-grey bark. The European beech Fagus sylvatica is the most commonly cultivated species, yielding a utility timber used for furniture construction, flooring and engineering purposes, in plywood, and household items. The timber can be used to build homes. Beechwood makes excellent firewood. Slats of washed beech wood are spread around the bottom of fermentation tanks for Budweiser beer. Beech logs are burned to dry the malt used in some German smoked beers. Beech is also used to smoke Westphalian ham, andouille sausage, and some cheeses.

In the fields of horticulture and botany, the term deciduous means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, after flowering; and to the shedding of ripe fruit. The antonym of deciduous in the botanical sense is evergreen.