Radioactive material is used worldwide for legitimate commercial purposes, including industrial processes in the oil and gas, aerospace, and food sterilisation sectors. Material used for these purposes is typically sealed in a metal capsule, such as stainless steel, titanium, or platinum, to prevent its dispersal and is commonly called a sealed source.1 Some of these sources are highly radioactive and are found in a wide variety of devices, ranging from mobile industrial radiography sources containing hundreds of curies of iridium-192 to larger irradiators with thousands, or even millions, of curies of cobalt-60. In the hands of terrorists, these sources could be used to produce a simple and crude, but potentially dangerous weapon, known as a radiological dispersal device or dirty bomb, whereby conventional The facilities where these sources are contained include, among other things, warehouses, commercial facilities, and research buildings. This book examines the challenges in reducing security risks posed by industrial radiological sources and the steps federal agencies are taking to improve security of the sources.