Increasing weed resistance to herbicides is a growing problem for agriculture, especially in emerging countries that are under more severe climatic constraints and suffer from negligible food surpluses. In a large number of cases, this resistance can be ascribed to an increase in the metabolism of the active molecules in the target plants. This metabolism involves in the first stage detoxification of herbicides by plants, and is most often dependent on oxygenases of the cytochrome P450 family of enzymes present and expressed in the target plant. Our goal is to advance our understanding of herbicide metabolism in plants by identifying the molecules produced by the plant. These investigations will guide chemical approaches for the development of synergistic molecules, new herbicides that are less easily metabolized by target plants.