The assumption that there is a significant connection between normal psychological and biological differences and the development of psychological disorders has grown in recent years and research in this area has developed rapidly. Written by psychologists with expertise in both the areas of abnormal and differential psychology, this textbook aims to integrate evidence and ideas from healthy personality and temperament on the one hand and psychological disorders on the other. This is achieved by viewing personality traits as predispositions to disorder, and by questioning how far the causes of various disorders can be seen as an extension or exaggeration of processes underlying normal personality or temperament. These main themes are discussed using a biological perspective, based on the theory that personality can be deconstructed into a number of basic dimensions (of biological origin) that also act as vulnerability factors for disorder. This is a second level textbook for undergraduate students of psychology, but it can also be used by health professionals and their trainees, psychiatrists, clinical psychologists and nurses.