This volume is concerned with metabolic reactions occurring in the nervous system. Some time ago, it was thought that since most of the intermediary metabolism that can be observed in the brain is not specific to this organ, there is little justification in studying neural metabolism as such. Later it was realized that for an understanding of neural functions, the understanding of metabolism in the brain and its alterations is essential. All aspects of the metabolism of a substrate in brain, or all metabolic reactions of the nervous system, could not be included in this volume; some will be dealt with in other volumes (such as the ones covering metabolic turn­ over, alterations of metabolism, or pathology). Review of the aspects covered here clearly shows that the study of metabolic reactions in the nervous system is a very active field, producing important results. As in so many areas of research, as we learn more, new aspects become known, new questions emerge, and we see that in solving some problems we open areas with many additional problems to solve. But the accomplishments to date are impressive and indicate further important advances in the future. Brain metabolism is more active, more plastic, and more comprehensive than previously estimated. It is an essential part of brain function, and with its alteration, brain function will be altered. This shows the importance of more knowledge in this area. It is hoped that this volume will be of assistance in such further studies.