The current understanding of iodine sources in the atmosphere, the abundance of atmospheric iodine compounds and their chemistry are reviewed. Besides CH3I, several other organic iodine compounds of biological origin, such as CH2I2, CH2ClI and C3H7I have been detected in ocean water. Due to their low solubility the water can become super-saturated with iodocarbons causing a flux from the aqueous to the gas phase. Anthropogenic sources of iodine in the atmosphere include the combustion of fossil fuels and the potential future use of halon replacements, such as CF3I. Data from measurements of iodine compounds in ocean water and the atmosphere are compiled. The atmospheric reaction cycles of iodine are described which comprise the photolytic decomposition of iodocarbons the interchange of iodine between the reservoir species and the interaction of iodine with aerosol particles. Depending on the concentration of reactive iodine in the troposphere, or the lower stratosphere, the photooxidant budget can significantly be affected and substantial ozone depletion is possible.