Basil UK (Ocimum basilicum), also called great basil or Saint-Joseph's-wort, is a culinary herb of the family Lamiaceae (mints).

It is also called the "king of herbs" and the "royal herb". The name "basil" comes from Greek βασιλικόν φυτόν (basilikón phutón), "royal/kingly plant".

Basil is possibly native to India, and has been cultivated there for more than 5,000 years. It was thoroughly familiar to the Greek authors Theophrastus and Dioscorides. It is a tender plant, best known as a culinary herb prominently featured in Italian cuisine, and also plays a major role in Southeast Asian cuisines of Indonesia, Thailand, Malaysia, Vietnam, Cambodia, Laos, and Taiwan. Depending on the species and cultivar, the leaves may taste somewhat like anise, with a strong, pungent, often sweet smell.

There are many varieties of Ocimum basilicum, as well as several related species or species hybrids also called basil. The type used in Italian food is typically called sweet basil (or Genovese basil), as opposed to Thai basil (O. basilicum var. thyrsiflora), lemon basil (O. × citriodorum), and holy basil (Ocimum tenuiflorum), which are used in Asia. While most common varieties of basil are treated as annuals, some are perennial in warm, tropical climates, including holy basil and a cultivar known as "African blue basil".

The various basils have such different scents because the herb has a number of different essential oils that come together in different proportions for various breeds. The strong clove scent of sweet basil is derived from eugenol, the same chemical as actual cloves. The citrus scent of lemon basil and lime basil reflects their higher portion of citral, which causes this effect in several plants including lemon mint, and of limonene, which gives actual lemon peel its scent. African blue basil has a strong camphor smell because it contains camphor and camphene in higher proportions. Licorice basil contains anethole, the same chemical that makes anise smell like licorice, and in fact is sometimes called "anise basil."