They are woody plants from 4 to 35 m tall (depending on species), and have stout shoots with resinous, often sticky, buds; opposite, palmately divided leaves, often very large (to 65cm across in Aesculus turbinata); and showy insect-pollinated flowers, with a single five-lobed petal (actually five petals fused at the base). The fruit is a rich glossy brown to blackish-brown nut, usually globose with one nut in a green or brown husk, but sometimes two nuts together in one husk, in which case the nuts are flat on one side; the point of attachment of the nut in the husk shows as a large circular whitish scar.

The most familiar member of the genus worldwide is the Horse-chestnut Aesculus hippocastanum, native to a small area of the Balkans in southeast Europe, but widely cultivated for its spectacular spring flowers (see photo, below). The yellow buckeye Aesculus flava (syn. A. octandra) is also a valuable ornamental tree with yellow flowers, but is less widely planted. Among the smaller species, the bottlebrush buckeye Aesculus parviflora also makes a very interesting and unusual flowering shrub. Several other members of the genus are used as ornamentals, and several horticultural hybrids have also been developed.

They are generally fairly problem-free, though a recently discovered leaf-mining moth Cameraria ohridella is currently causing major problems in much of Europe, causing premature leaf fall which looks very unattractive. The symptoms (brown blotches on the leaves) can be confused with damage caused by the leaf fungus Guignardia aesculi, which is very common but usually less serious.

Buckeyes are poisonous, but some native American tribes leached the pulverized nuts to make them edible. California buckeyes are known to cause poisoning of honeybees from toxic nectar. Other buckeye species are thought to have the same effect, but the toxins are diluted because the tree is not so predominant in any one area.

In Britain, the nuts of A. hippocastanum are used for the popular childrens' game conkers. The wood is fairly soft and little-used.

The Ohio buckeye is the state tree of Ohio.