How can we understand and explain human behaviour? This is a basic question that is asked by students taking courses in psychology, medicine and health studies as well as colleagues in human services. Generally speaking, human behaviour is understood in terms of three broad perspectives – biology, psychology and sociology. Under the biological perspective, human behaviour is seen as a product of biological structures and mechanisms. Under the psychological perspective, human behaviour is seen as a result of mental processes, which may or may not have biological bases. Finally, sociologists believe that external social structures and processes determine human behaviour. External environmental factors such as poverty, income inequality and alienation contribute to substance abuse and will be addressed in this intriguing book on human development.