This book offers a comprehensive overview of the most important neurochemicals and approaches everything from the neurochemical’s perspective. It attempts to integrate the biochemical pathways of synthesis and metabolism of these neurochemicals with the disease states and point out the avenues of diagnostic testing and therapeutic intervention. Each chapter focuses on a specific neurochemical and provides a brief history, the biochemical profile, metabolism, physiological functions, and the clinical aspects. The clinical part of each chapter includes a discussion on disease states with either increased or reduced activity of the neurochemical and either activation or inhibition of the relevant receptors. This book is targeted toward practitioners and students of neuroscience and is written to emphasize the importance of these neurochemicals in the brain. With this emphasis on background neurochemical processes, the readers will be pointed towards logical diagnostic studies, laboratory investigations, and therapies based on the neurochemical dysfunction that underlies various disease states.