This volume addresses a broad spectrum of the environmental issues surrounding organic bromine and iodine compounds. It covers their partition among the environmental compartments and the potential for their long-range dissemination. The important issue of their atmospheric chemistry is discussed in detail in the context of ozone depletion and global warming, and the significant difference between the reactions of methyl bromide and methyl iodide are underscored. The mammalian toxicity is discussed and the mechanisms of the degradation and transformation of organic bromine and iodine compounds addressed. There has been considerable interest in naturally occurring metabolites in the current debate on the fate and partition of methyl bromide that is an important fungicide and is produced in substantial quantities as a metabolite of marine algae. The possible natural occurrence of diphenyl ethers that are used as flame retardants have also been raised. A discussion is given on plausible mechanisms for the biosynthesis of representative organic bromine and organic iodine metabolites. Reaction pathways are illustrated throughout and comprehensive references are given.