Why is it that one person can become severely dependent on drugs or alcohol, whereas another, although exposed to the same environment and experiences, does not? This book describes a series of studies that were conducted in order to examine this vulnerability to addictive behaviour. The book demonstrates how genetic variants, personality traits and responsiveness to substance- related stimuli can influence an individual''s propensity toward a severe dependency on drugs. Ultimately, this book explains the importance of genetic variation in substance dependence; it advances our understanding of the personalities of substance abusers and increases our knowledge of neurobehavioural influences on addiction, thus offering a multidisciplinary approach to the study of vulnerability factors to substance dependence. This book adopts a biopsychosocial approach to addiction and should be of particular use to both professionals and students in the field of Addiction as well as to those in Psychology, Health sciences, Counselling and related disciplines.