The totality of an individual’s behavioural and emotional characteristics are their personality traits. Personality embraces a person’s moods, attitudes, opinions, motivations, and style of thinking, perceiving, speaking, and acting. It is part of what makes each individual distinct. Theories of personality have existed in most cultures and throughout most of recorded history. This book discusses current research in the study of personality traits, including addictive disorders and personality disorders; cognitive and biological markers of schizophrenia; the genetics of personality disorders; and optimistic or pessimistic personality traits.