Publisher Summary Polycyclic aromatic hydrocarbons (PAHs) represent an important class of environmental pollutants. They are present in fossil fuels and are formed upon incomplete combustion and pyrolysis of organic matter. The carcinogenic potential of PAHs, which are mostly nontoxic, is caused by enzymatic activation. As parent PAHs are lipophilic substances, they need biotransformation to water-soluble derivatives before they can be efficiently excreted from the mammalian organism. This detoxification process converts them to a variety of reactive metabolites amongst which epoxides have a special importance. The enzymes involved are classified in two categories: (1) phase 1 enzymes, which catalyze oxidative reactions, and (2) phase 2 enzymes, which catalyze conjugative reactions of oxidized PAHs with endogenous compounds such as sulfuric acid, glucuronic acid, and glutathione. The various PAH metabolites may be excreted from the organism either as free or as conjugated compounds. To enable excretion of the water-insoluble polycyclic aromatic hydrocarbons from living cells, they are metabolized to oxygenated products.