A vast empirical literature has established the importance of the therapist’s and client’s personality to treatment outcome. In this 1hr 50min lecture, Dr. McWilliams reviews ten different psychological lenses through which personality has been viewed (temperament, attachment, observed clinical pattern, defensive structure, affective organization, implicit cognition, drive tendencies, self-definition versus self-in-relation orientation, core relational theme, level of severity). She reviews the evidence base for each angle of vision, explores some therapeutic implications of each perspective, and gives clinical examples.