The Second Edition of the Handbook of Neurochemistry, which was published about 24 years ago, consisted of 10 volumes. The present, Third Edition, The Handbook of Neurochemistry and Molecular Biology, is over twice as large; indicating a great expansion of neuroscience in the past two decades. We now have not only more data on brain mechanisms relating to behavior (mental activity and cognitive processes), but we understand in some detail the mechanisms of these functions. The past editions focused purely on neurochemical aspects - the new edition reflects the need of interdisciplinary approach for understanding neural mechanisms. In addition to metabolic processes, the 17 new volumes explore the functions of peptides, transport, immunology and other processes not well understood 24 years ago. Several volumes deal with pathological changes and with repair and therapy of both mental and neurological pathologies. The purpose of this edition is to provide an evaluation of the results of investigations; to serve as a guide rather than enumerating all the available findings in detail - it indicates future possibilities and the existing knowledge in neuroscience. The significance of understanding neural processes needs no emphasis - its potential is primary in mental and neural pathology, but also in physiological importance. The volumes should serve as an aid to researchers expanding our knowledge and to educators training the next generation of neuroscientists and clinicians.