The illegal drug trade, drug trafficking, or narcotrafficking is a global black market dedicated to the cultivation, manufacture, distribution and sale of prohibited drugs. Most jurisdictions prohibit trade, except under license, of many types of drugs through the use of drug prohibition laws. The think tank Global Financial Integrity's Transnational Crime and the Developing World report estimates the size of the global illicit drug market between US$426 and US$652 billion in 2014 alone. With a world GDP of US$78 trillion in the same year, the illegal drug trade may be estimated as nearly 1% of total global trade. Consumption of illegal drugs is widespread globally, and it remains very difficult for local authorities to reduce the rates of drug consumption.

A black market, underground economy, or shadow economy is a clandestine market or series of transactions that has some aspect of illegality or is not compliant with an institutional set of rules. If the rule defines the set of goods and services whose production and distribution is prohibited or restricted by law, non-compliance with the rule constitutes a black-market trade since the transaction itself is illegal. Such transactions include the illegal drug trade, prostitution, illegal currency transactions, and human trafficking.