Plants small to large trees, monoecious. Leaves alternate, short- to moderately long-petiolate. Leaf blades 1 time pinnately compound, the leaflets unlobed, pinnately veined, the margins toothed. Stipules absent. Staminate and pistillate inflorescences separate, with small bracts (and usually also minute bractlets) subtending and sometimes partially fused with each other and/or to the flowers, the staminate flowers in long, pendent, solitary or clustered catkins produced near the base of the current-year’s growth, the pistillate flowers solitary or in very short spikes produced near the tip of the current-year’s growth. Flowers actinomorphic, imperfect, the pistillate ones epigynous. Staminate flowers with the calyx absent or minutely 4-lobed; corolla absent; the stamens mostly 3–50, with a short filament and the anther attached at its base. Pistillate flowers with the calyx absent or minutely 4-lobed; corolla absent; stamens and staminodes absent; the ovary inferior (but sometimes appearing naked in the absence of a perianth), usually 2-locular toward the base but appearing 1-locular toward the tip, with 1 ovule, the placentation basal. Styles usually 2 (sometimes united basally), relatively stout and spreading, each with an expanded stigmatic region along the upper side. Fruits nuts, enclosed in a thick, fleshy to leathery or woody husk. About 8 genera, about 60 species, North America to South America, Europe, Asia, Pacific Islands.

The Missouri genera of this family all have large, oil-rich nuts that are an important food for wildlife, and have been important food for humans in the past. Various species are larval food plants for a variety of butterflies and moths, including the banded hairstreak butterfly (Satyrium calanus (Hübner)), walnut sphinx moth (Amorpha juglandis (J.E. Sm.)), luna moth (Actias luna (L.)), various underwing moths (Catocala spp.), dagger moths (Acronicta spp.), one-spotted variant moth (Hypagyrtis unipunctata (Haw.)), and giant regal moth (Citheronia regalis (Fabr.)) (Heitzman and Heitzman, 1987; Kurz, 2003). The last of these produces the largest caterpillar in the United States, the hickory horned devil, a fierce-looking green creature that can grow to nearly 15 cm in length. Members of the Juglandaceae are among the last trees to leaf out in the spring and among the first to lose their leaves in autumn.