The walnut is the edible seed of deciduous trees belonging to the Juglandaceae family. There exist at least thirty different cultivars of walnut. The three popular varieties grown for their commercial purpose are the English, or Persian, walnut (Juglans regia), the Black walnut (Juglans nigra), and the White, or Butternut, walnut (Juglans cinerea). The walnut tree can reach a height of twenty-five meters and, depending on the climate, may only start bearing fruit after five to ten years. In California, where most walnuts come from, harvesting starts in August.

The walnut fruit is wrapped in a green and fleshy husk. Walnut fruits are ready for harvesting when this green hull starts to crack open, exposing the light brown, hard-shelled walnut inside. The walnut kernel consists of two uneven, corrugated lobes, off-white in colour and covered by a papery thin, light brown layer. The lobes are partially attached to each other. Drying the nut is an extremely accurate process, as this is linked with shelf life.

Walnuts might be eaten plain raw from the shell, but also roasted, salted or sweetened. Crushed kernels are used to be sprinkled over salads, deserts, sundaes or pies.

The seeds contains a high source of nutrients, especially proteins. Studies show that walnuts positively affect cardiovascular diseases. Walnuts lower blood cholesterol. The walnut is very popular in the food industry, as well can be eaten as snacks.