After the completion of the first edition of this series, this editor thought that a new edition would not be warranted in less than IS, perhaps 20, years, but it seems that we live in a time in which rapid changes are the norm and findings in a field such as neurochemistry develop exponentially. The task of a future editor attempting to get a comprehensive neurochemical handbook for the year 2000 would be even less enviable, but by then information processing may be very different. The approach, the design, and the areas covered by each volume and each chapter are necessarily arbitrary, and it is likely that other editors or authors would have approached the coverage or the organization in a different manner. It is hoped, however, that readers will find the series helpful for beginning or for continuing work. There may be some overlap among the various chapters, but insisting on single coverage of an area would at times have restricted treatment to only one point of view and might have truncated and hurt the logical flow of some of the chapters.