Nitroaromatic compounds are abundantly present in nature, but are in most cases highly toxic to living organisms. Several microorganisms, however, are capable of mineralizing or converting these compounds. Until now four pathways for the complete degradation of nitroaromatics have been described, which start with either the oxygenolytic or reductive removal of the nitro group from the aromatic ring or with this removal by means of replacement reactions. Besides these conversions many organisms are able to reduce nitroaromatics. The degradation of nitroaromatic compounds does not only occur in pure cultures but also in situ, for example in soil, water and sewage. However, several problems are associated with the application of microorganisms in the bioremediation of contaminated sites, as nitroaromatics or their conversion products may chemically interact with soil particles and cells. Besides the possibilities of applying microorganisms in the cleaning of sites contaminated with nitroaromatics, the use of microorganisms or enzymes in the biocatalytic production of industrially valuable products from nitroaromatics is also discussed.