Fissile material -- highly-enriched uranium (HEU) or weapon-grade plutonium -- is the critical ingredient in building a nuclear weapon.  Most experts agree that terrorists are not able to produce fissile material, but a reasonably sophisticated terrorist organization could make a crude nuclear weapon, or improvised nuclear device (IND), if it stole or acquired a sufficient quantity and quality of such material.  Therefore, combating smuggling of weapons-usable nuclear materials is vital to preventing terrorists from acquiring nuclear weapons.

Other radioactive materials that could not be used to create a nuclear explosion could still be used in a radioactive dispersal device (RDD), or "dirty bomb."  An attack with such a device would be less significant than a nuclear attack, but its probability is higher and, given sufficient quantity and radioactivity of the material involved, the damage could still be significant.  Therefore, combating the smuggling of these materials is also important.

The International Atomic Energy Agency (IAEA) maintains a database of illicit nuclear trafficking incidents around the world.  Since 1993, the IAEA has recorded more than 1,000 confirmed reports on incidents involving smuggling, theft, loss and illegal disposal, illegal possession and transfer, or attempted illegal sales of nuclear or radioactive materials.  This included 149 incidents in 2006.