This chapter compares the viewpoint that traits are an inclusive set of dispositions shared by all people against a different viewpoint that an individual's underlying traits are exclusive to only that particular person. It examines the comparison that is made between psychodynamic perspectives and cognitive theories. The chapter addresses the issue of the role of biology versus experience on personality, examining evidence of inherited temperamental differences between individuals and discusses how experience and nature interact in the development of personality across the lifespan. It discusses a set of theories and research about personality that can be subsumed under the umbrella of positive psychology. Personality psychologists are concerned with the consistent patterns of thoughts, feelings and behaviours that differentiate people from each other. Personality traits form the conceptual bedrock of personality psychology. The neo-Freudians continued to emphasize the significance of unconscious motives, conflicts existing within the psyche and the role of early experiences in shaping personality.