Clandestine chemistry is chemistry carried out in secret, and particularly in illegal drug laboratories. Larger labs are usually run by gangs or organized crime intending to produce for distribution on the black market. Smaller labs can be run by individual chemists working clandestinely in order to synthesize smaller amounts of controlled substances or simply out of a hobbyist interest in chemistry, often because of the difficulty in ascertaining the purity of other, illegally synthesized drugs obtained on the black market. The term clandestine lab is generally used in any situation involving the production of illicit compounds, regardless of whether the facilities being used qualify as a true laboratory.

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.