Cytochromes P-450 (P-450s) constitute a large family of oxygenases catalyzing phase I metabolism of various xenobiotics, including pesticides. In most cases, they mediate reactions resulting in detoxification of the parent molecule. Plant P-450s play an important role in herbicide metabolism, by constituting a key factor of herbicide selectivity, and of herbicide resistance recently observed in some weed biotypes. Definitive proof of P-450-mediated pesticide metabolism in filamentous fungi has not yet been obtained. However, indirect evidence supports such an hypothesis. The detoxification and degradation potential of P-450s from plants or microorganisms could be exploited for bioremediation of water, industrial waste, and soil contaminated with pesticides. A more comprehensive knowledge of these enzymes, including functional characterization of genes and proteins, remains necessary for an efficient management of P-450 potentialities.