The illegal drug trade or drug trafficking is a global black market consisting of the cultivation, manufacture, distribution and sale of illegal drugs. While some drugs are legal to possess and sell, in most jurisdictions laws prohibit the trade of certain types of drug.

The illegal drug trade operates similarly to other underground markets. Various drug cartels specialize in the separate processes along the supply chain, often localized to maximize production efficiency. Depending on the profitability of each layer, cartels may vary in size, consistency, and organization. The chain ranges from low-level street dealers who may be individual drug users themselves, through street gangs and contractor-like middlemen, up to multinational empires that rival governments in size.

Illegal drugs may be grown in wilderness areas, on farms, produced in indoor or outdoor residential gardens or indoor hydroponic grow-ops, or manufactured in drug labs located anywhere from a residential basement to an abandoned facility. The common characteristic binding these production locations is that they are discreet to avoid detection, and thus they may be located in any ordinary setting without raising notice. Much illegal drug cultivation and manufacture takes place in developing nations, although production also occurs in the developed world.

In locales where the drug trade is illegal, police departments as well as courts and prisons may expend significant resources in pursuing drug-related crime. Additionally, through the influence of a number of black market players, corruption is a problem, especially in poorer societies.

Consumption of illegal drugs is widespread globally. While consumers avoid taxation by buying on the black market, the high costs involved in protecting trade routes from law enforcement lead to vastly inflated prices.

Additionally, various laws criminalize certain kinds of trade of drugs that are otherwise legal (for example, untaxed cigarettes). In these cases, the drugs are often manufactured and partially distributed by the normal legal channels, and diverted at some point into illegal channels.

Finally, many governments restrict the production and sale of large classes of drugs through prescription systems.