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The chemistry and transport of iodine in light-water reactor (LWR) containment are best viewed as a dynamic system in which iodine species enter from the reactor coolant system and interact with a complex gas mixture, with transport to and from surfaces and aqueous solutions. Iodine would enter containment as some combination of cesium iodide (CsI), hydrogen iodide (HI), elemental iodine atoms (I2), silver iodide (AgI), and perhaps some organic iodide. The containment atmosphere would consist of steam, air, hydrogen, some hydrocarbons, aerosol material, other fission products in various chemical forms, and the iodine species. The containment atmosphere is in contact with water pools, water films, surfaces, and, in some cases, with sprays. The ultimate aim of a description of iodine behavior in severe LWR accidents is a time-dependent accounting of iodine species released into containment and to the environment. Factors involved in the behavior of iodine can be divided into four general categories: initial release into containment, interaction of iodine species in containment not directly involving water pools, interaction of iodine species in, or with, water pools, and interaction with special systems such as ice condensers or gas treatment systems