Fraxinus is a genus of flowering plants in the olive and lilac family, Oleaceae. It contains 45-65 species of usually medium to large trees, mostly deciduous though a few subtropical species are evergreen.The leaves are opposite (rarely in whorls of three), and mostly pinnately compound, simple in a few species. The seeds, popularly known as keys or helicopter seeds, are a type of fruit known as a samara. Rowans or Mountain Ashes are unrelated to true ashes and belong to the Genus Sorbus though the leaves and buds are superficially similar.

Ash is a hardwood and is hard, dense (within 20% of 670 kg/m³ for Fraxinus americana, and higher at 710 kg/m³ for Fraxinus excelsior), tough and very strong but elastic, extensively used for making bows, tool handles, baseball bats, hurleys.

It makes excellent firewood and barbecue or smoking wood. The two most economically important species for wood production are White Ash in eastern North America, and European Ash in Europe.