Interpol launched Project Geiger in 2005 to counter the threats posed by criminal or terrorist use of radioactive materials. Weapons grade materials are highly protected but other radioactive materials such as cesium-137, polonium-210 and strontium-90 are used in a wide variety of contexts from hospitals to mines and are far less well secured. This article describes known cases of theft in Europe and North America, incidents in which radioactive materials were used, and the efforts being made to reduce the risk of such materials falling into terrorist hands.