Arms trafficking or gunrunning is the illicit trade of contraband small arms, explosives, and ammunition, which constitutes part of a broad range of illegal activities often associated with transnational criminal organizations. The illegal trade of small arms, unlike other organized crime commodities, is more closely associated with exercising power in communities instead of achieving economic gain. Scholars estimate illegal arms transactions amount to over US$1 billion annually.

To keep track of imports and exports of several of the most dangerous armament categories, the United Nations, in 1991, created a Register for Conventional Arms. Participation, however, is not compulsory, and lacks comprehensive data in regions outside of Europe. Africa, due to a prevalence of corrupt officials and loosely enforced trade regulations, is a region with extensive illicit arms activity. In a resolution to complement the Register with legally binding obligations, a Firearms Protocol was incorporated into the UN Convention on Transnational Organized Crime, which requires states to improve systems that control trafficked ammunition and firearms.

The 1999 Report of the UN Panel of Governmental Experts on Small Arms provides a more refined and precise definition, which has become internationally accepted. This distinguishes between small arms (revolvers and self-loading pistols, rifles and carbines, submachine guns, assault rifles, and light machine guns), which are weapons designed for personal use, and light weapons (heavy machine guns, hand-held under-barrel and mounted grenade launchers, portable anti-aircraft guns, portable anti-tank guns, recoilless rifles, portable launchers of anti-aircraft missile systems, and mortars of calibres less than 100 mm), which are designed for use by several persons serving as a unit. Ammunition and explosives also form an integral part of small arms and light weapons used in conflict.