This publication is based on the plant processes and reaction sites for which reliable knowledge on both their physiology and biochem-istry and the mode of herbicidal action is available. Targets of the agrochemical research, such as enzymes of biosynthetic pathways or herbicide-binding peptides in the photosynthetic membrane, are highlighted. Detailed knowledge about the target sites will allow bio-chemical model systems to evaluate the biological activity of newly synthesized compounds before their conventional screening in the greenhouse. Quantitative structure/activity relationships should be performed more reliably with simple biological species or enzymol-ogy assays, to aid in the rational design of pesticides. This text is highly valuable for plant physiologists, pathologists, and chemists in the agrochemical industry and universities.