Xenobiotics (foreign chemicals) are natural or synthetic substances (such as pesticides) that cannot be utilized by plants in their energy-yielding metabolism. The main enzymatic reactions used by plants for xenobiotic detoxification include oxidation, reduction, hydrolysis, and conjugation with glutathione, sugars and amino acids. Xenobiotic conjugates may be compartmentalized in the vacuole of plant cells by means of membrane-bound transporters. This text includes discussion of current advances associated with the regulation of gene expression and enzymology of the major classes of xenobiotic degrading enzymes. Genetic engineering of crops with plant or bacterial detoxification genes and chemical regulation of the enzymatic systems that detoxify xenobiotics in plants by herbicide safeners and synergists are also discussed. Advanced level and graduate students and professional scientists in agronomy, plant physiology, biochemistry, molecular biology, chemistry should find this text useful.