Book excerpt: The NATO Advanced Research Workshop (ARW) on "Regulation of Enzymatic Systems Detoxifying Xenobiotics in Plants" intended to provide a forum to scientists from academia, industry, and govemment for discussing and critically assessing recent advances in the field of xenobiotic metabolism in plants and for identifying new directions for future research. Plants function in a chemical environment made up of nutrients and xenobiotics. Xenobiotics (foreign chemicals) are natural or synthetic compounds that can not be utilized by plants for energy-yielding metabolism. Plants may be exposed to xenobiotics either deliberately, due to their use as pesticides or accidentally, from industrial, agricultural, and other uses. Plants, like most other organisms, evolved a remarkable battery or metabolic reactions to defend themselves against the potentially toxic effects of xenobiotics. The main enzymatic reactions utilized by plants for xenobiotic detoxification include oxidation, reduction, hydrolysis and conjugation with glutathione, sugars (e.g., glucose), and amino acids. Eventually, xenobiotic conjugates are converted to insoluble bound residues or to secondary conjugates, which are deposited in the vacuole of plant cells.