Forensic psychiatrists use their scientific and clinical expertise to evaluate civil, criminal, correctional or legislative matters.
Forensic psychiatry patients are often classified into three categories:
- Mental illness
 - Psychosis or personality disorder
 - Substance or illicit drug addiction
 
The goal of a forensic psychiatrist is to build an understanding of how mental health affects those who have committed a crime and how this should influence sentencing or other consequences within the legal system.