In chapter 4, we considered biological roots of crime, including the influence of genetic inheritance, the brain and central nervous system, and hormonal and other physiological mechanisms that influence aggression and violence. In this chapter, we introduce the psychological theories that attribute the roots of crime to mental processes that develop as people interact with their families and others. We focus on the major psychological theories of personality and personality development as well as on theories about how people process information, think, learn, and interact with others. We then apply these concepts as we trace the development of crime and mental disorders in chapters 7, 8, and 9.