Plants shrubs or more commonly small to large trees, monoecious. Leaves alternate, mostly short-petiolate. Stipules present, membranous to papery or scalelike, often shed early. Leaf blades simple, unlobed or pinnately to rarely nearly palmately lobed, pinnately to rarely nearly palmately veined, the margins entire or toothed. Staminate and pistillate inflorescences separate or with pistillate flowers near the base and staminate flowers above them, with small bracts subtending at least the staminate flowers, consisting of heads or spikelike catkins or the pistillate flowers sometimes solitary, paired, or in small clusters. Flowers actinomorphic, imperfect, the pistillate ones epigynous. Staminate flowers with the calyx of (3)4–6(–8) lobes or sepals; corolla absent; the stamens (2–)6–18 or rarely more, free, with a slender filament and the anther attached at its base (but often in a deep basal notch); a rudimentary, nonfunctional pistil often present. Pistillate flowers with the calyx absent or more commonly of 4–6 lobes or sepals; corolla absent; stamens and staminodes absent; the ovary inferior (but sometimes appearing naked in the absence of a perianth), usually 3- or 6-locular, but occasionally appearing 1-locular toward the tip, with 2 ovules per locule, the placentation axile. Styles usually 3, flattened and often expanded laterally toward the tip, spreading, each with a stigmatic region along the upper side, sometimes only near the tip. Fruits nuts, these solitary or in clusters of 2–4, partly or completely enclosed in a leathery to woody cupule with a spiny or scaly outer surface. Ten or 11 genera, about 800 species, throughout the northern hemisphere temperate zone and in mountains in the northern hemisphere tropics.

Members of the Fagaceae are dominant trees in most Missouri forests. Many species produce valuable timber. The nuts are large and rich in oils. They are edible and nutritious, and are among our most important foods for wildlife, such as mammals, birds, and a large diversity of insects and other invertebrates.