This volume is concerned with the enzymes of the nervous system. Cerebral enzymes form the basis of the functional brain. They are needed for the control of the energetics of the nervous system, whether it be their release or their direction; for the elaboration of transmitters and for their destruction; for the synthesis, transport, and breakdown of all metabolites of the nervous system. They are indispensable for the control of the multitude of factors that govern our thinking and our behavior. They make it possible for us to comprehend what is taking place around us and perhaps to understand what may be in store for us. Enzymes are the stuff of life, and no living cell can be without them. They are the results of many millions of years of evolution, from the time when biological membranes first came into being and were folded to produce the first cells within which the earliest enzymes were wrought. Countless changes have taken place within them, so that, now, only those enzymes exist that play specific roles in the functions of the living cells of today. Those in the nervous system possess a mUltiple role: in the creation, maintenance, and ultimate breakdown of the component cells and in enabling consciousness, perception, memory, and thought to become possible. But though life may go on forever, the enzymes that make life possible will undergo the many changes involved in the evolutionary process.