The Persian Walnut (Juglans regia) is a walnut native from the Balkans in southeast Europe east through southwest and central Asia and the Himalaya to southwest China.

It is a large deciduous tree attaining heights of 25-35 m, and a trunk up to 2 m diameter, commonly with a short trunk and broad crown, though taller and narrower in dense forest competition. It is a light-demanding species, requiring full sun to grow well. The bark is smooth silvery-grey, with scattered broad fissures with a rougher texture. Like all walnuts, the pith of the twigs contains air spaces. The leaves are alternate, 25-40 cm long, odd-pinnate with 5-9 leaflets, the largest leaflets the three at the apex, 10-18 cm long and 6-8 cm broad; the basal pair of leaflets much smaller, 5-8 cm long. The male flowers are in drooping catkins 5-10 cm long, the female flowers terminal, in clusters of two to five, ripening in the autumn into a fruit with a green, semi-fleshy husk and a brown corrugated nut. The whole fruit, including the husk, falls in autumn; the seed is large, with a relatively thin shell, and edible, with a rich flavour.

The Persian Walnut was introduced into western and northern Europe very early, by Roman times or earlier, and to the Americas by the 17th century. Importand nut-growing regions include France, Greece, Bulgaria and Romania in Europe, China in Asia, California in North America and Chile in South America. It is cultivated extensively for its high quality nuts, eaten both fresh and pressed for their richly flavoured oil. The wood is of very high quality, similar to American Black Walnut, and is used to make furniture and rifle stocks.

The name Persian indicates its origins in Persia (southwest Asia); 'walnut' derives from the Germanic wal-, "foreign", recognising that it is not native in northern Europe. The scientific name Juglans is from Latin jovis glans, "Jupiter's nut", and regia, "royal". In the United States, the Persian Walnut is commonly mis-named "English Walnut"; the species is not native in England.