When confronting the reality of crime in society, you may encounter a focus on the “what”—that is, on the frequency and type of crime. This, coupled with an emphasis on restoring order in society, may leave you wondering about the “why,” or what led up to the occurrence of a crime. If one considers that crimes may not occur spontaneously—that a series of events may lead to crime as an outcome of many variables—then answering “why” becomes an important aspect of crime prevention. Criminology is the part of the criminal justice system that seeks to discover the “why” behind criminal behavior. Criminologists use the scientific method and inquire about the aspects of human behavior that lead to crime. This week, you focus on the theories that criminologists and other behavioral scientists have used and currently use to explain the causes of criminal behavior. This week, you explore how criminal justice professionals understand and react when encountering persons with mental illness. You may be wondering how the behavioral and criminological theories covered in your readings this week relate to your criminal justice professional practice. If you ascribe to the equation that a person will choose whatever meets a need or brings pleasure unless deterred, whether legal or illegal, then you may consider your working environment in a particular way. Or, you may view such a scenario differently through the perspective that the choices available in society influence the choices any individual might make. In this Discussion, you consider how to apply theory in criminal justice practice.