Tobacco is a product processed from the dried leaves of plants in the genus Nicotiana. It can be used as a pesticide, and extracts form ingredients of some medicines, but is most commonly consumed as a drug. Tobacco is a name for any plant of the genus Nicotiana of the Solanaceae family (nightshade family) and for the product manufactured from the leaf used in cigars and cigarettes, snuff, pipe tobacco, chewing tobacco, and flavored shisha. Tobacco plants are also used in plant bioengineering, and some of the more than 70 species are grown as ornamentals. The chief commercial species, N. tabacum, is believed native to tropical America, like most nicotiana plants, but has been so long cultivated that it is no longer known in the wild. N. rustica, a species producing fast-burning leaves, was the tobacco originally raised in Virginia, but it is now grown chiefly in Turkey, India, and Russia. The addictive alkaloid nicotine is popularly considered the most characteristic constituent of tobacco but the harmful effects of tobacco consumption can also derive from the thousands of different compounds generated in the smoke, including polycyclic aromatic hydrocarbons (such as benzopyrene), formaldehyde, cadmium, nickel, arsenic, tobacco-specific nitrosamines (TSNAs), phenols, and many others.

In consumption it most commonly appears in the forms of smoking, chewing, snuffing, or dipping tobacco. Tobacco had long been in use as an entheogen in the Americas, but upon the arrival of Europeans in North America, it quickly became popularized as a trade item and a widely abused drug. This popularization led to the development of the southern economy of the United States until it gave way to cotton. Following the American Civil War, a change in demand and production techniques allowed for the development of the cigarette. This new product quickly led to the growth of tobacco companies.