Shipments of weapons are made illegally by governments and private arms dealers. Government shipments are sometimes covert military assistance and may break international treaties. Illegal private arms deals are done for profit; dealers may supply governments, gangs or revolutionary groups. Terrorist organizations and drug trafficking gangs have established their own illegal arms distribution networks. Arms illegally shipped have ranged from jet fighters, radar, computer-controlled weaponry and intelligence gathering systems to bombs, bullets and explosives of all kinds. No instance of illegal nuclear or biological weapons shipments is known, but the control of uranium and its by-products used for nuclear weaponry is lax and it is suspected that there has been illegal appropriation of nuclear materials from energy-generating and research projects to weaponry research, if not to weapon manufacture

The black-market trade in small arms and light weapons today sustains bloody conflicts around the world and arms criminals, terrorists and drug-traffickers. As a result, large areas of the world have become extremely dangerous for civilians, relief and development workers, business people and peacekeepers

The initiation or continuation of internal and ethnic conflicts generates a demand for multiple and varied sources of light weapons, including illicit sources. These two factors reinforce one another: the availability of arms facilitates the outbreak of a conflict, which produces a demand for more arms and ammunition; this, in turn, encourages existing suppliers to expand their offerings and draws new suppliers into the marketplace

In Sweden in 1987 it was discovered that major Swedish armaments companies had been smuggling high technology weaponry and munitions to black-listed countries for nearly a decade. In September 1990, Germany was investigating 60 companies suspected of making arms-related sales to Iraq, including the precursors and technology for chemical weaponry

In 1995, US officials believed they could prove irrefutably that China shipped M-11 ballistic missiles to Pakistan in violation of Beijing's commitment not to do so