Herbicides are part of modern agricultural production systems and therefore contribute significantly to the economy of agricultural products. At the same time, herbicides are potent and specific inhibitors of plant metabolism and may therefore be used as valuable tools in basic plant physiological research. A well-known example is the photosynthesis-inhibiting herbicide diuron, known to plant physiologists as DCMU, which has become one of the essentials in modern photosynthesis research. Similarly, knowledge in other areas of plant metabolism may be advanced by the use of herbicides as specific inhibitors. This book describes the effects of herbicides on the metabolism of higher plants from the viewpoint of the plant physiologist. The material of this book is therefore, as far as possible, divided into areas of metabolism. This book intends (1) to present the reader with current knowledge and views in the area of herbicide modes of action and (2) to promote the future use of herbicides as metabolic inhibitors in plant physiological research to the advantage of both, the pesticide and the plant sciences. I wish to express my thanks to my colleagues and friends Prof. N. Amrhein, Prof. E. Elstner, Dr. L. Eue, Dr. J. Konze, Dr. K. Liirssen, Dr. W.Oettmeier, Dr. H. Quader, Dr. R. R. Schmidt, Dr. R. H. Shimabukuro, Dr. J. Stetter, Prof.