This book includes a series of reviews on general aspects of biomarker use in the study of psychiatric and neurodegenerative diseases and the development of medications involved in their treatment. It describes the pros and cons of the various approaches and covers the successes and failures in this research field. It is only by a thorough understanding of the shortcomings that progress can be made. The overall goal is to facilitate the understanding and treatment of these disorders, by providing a viable mechanism of catching up with other areas of modern medicine, such as diabetes and heart disease. Finally, it is anticipated that the development and application of valid biomarker tests and the leveraging of novel drug targets will help the fields of psychiatry on neurodegenerative disorders move into the area of personalized medicine where the right patients can receive the right medication at the right time for the best possible outcome.