In this chapter, nomenclature for radicals, ions and related species is described. Radicals were previously called ‘free radicals' to distinguish them from substituent prefixes which formerly were also called radicals. The rules for naming radicals and ions are based on the same principles as those of organic compounds defined in previous chapters. Parent hydrides and parent compounds are selected and modified using specific suffixes (called cumulative suffixes) and prefixes; traditional endings are used to describe anions derived from acids and related compounds. Nomenclature for zwitterions and radical ions is also described.