This book presents a thorough and critical review of current knowledge about the age of onset of mental disorders. The opening chapters offer information about the impact of the age of onset on the clinical picture, course, and outcome of physical illnesses, and about the neurobiological implications and correlates of different ages of onset. The impact and correlates of the ages of onset of all the most important mental disorders are then discussed in detail by internationally renowned scientists. The background to the book is the recognition that a better understanding of age of onset makes it possible to estimate the lifetime risk of disorders, helps to elucidate pathogenesis, and facilitates efficient, targeted clinical management. The book will be of value for clinicians, mental health professionals, mental health researchers, epidemiologists, and different stakeholders in the mental health field.