This volume presents the progress made in the study of the mode of action of phytotoxic compounds that have been developed as herbicides in the past. The 13 chapters are written by experts in herbicide research and development, chemists, biochemists and plant physiologists. The biochemistry of the target enzymes is described together with model assays, molecular genetics and special reference to transgenic herbicide-resistant crops. Additional chapters deal with synthetic chemical pathways, chirality effects found in certain herbicide classes and transcuticular pesticide penetration.