The diversion to military programmes of materials and technologies obtained from foreign suppliers for peaceful purposes has played a prominent role in the known cases of nuclear proliferation. The need to strengthen nuclear export controls has been identified by the G8 group of industrialized states and the European Union. This study examines the structure and activities of the Nuclear Suppliers Group (NSG), a group of 45 states committed to applying effective controls on exports of an agreed set of items as part of a wider effort to prevent nuclear proliferation.