The assessment of personality provides the clinician with an opportunity to gather idiosyncratic information about an individual; information that is potentially useful in the diagnosis, treatment, and prognosis of that patient. In the area of psychopathology, personality has been viewed historically within the context of categorical diagnoses of personality disorder. This thesis critically reviews a recently proposed theory of personality that has incorporated normal and abnormal personality into a dimensional system of classification. The biosocial theory of personality and in its expanded form, the psychobiological model of temperament and character, were proposed by C.R. Cloninger and his colleagues in an attempt to provide a theoretical base from which to test causal hypotheses about personality in psychopathology. The theory is discussed in terms of its relevance to the understanding of personality structure, development, and psychopathology. It is concluded that despite limitations, this theory has an important contribution to make to further research investigating the influence of personality variables in a clinical setting.