Forensic psychology is the intersection between psychology and the justice system. It involves understanding fundamental legal principles, particularly with regard to expert witness testimony and the specific content area of concern (e.g., competence to stand trial, child custody and visitation, or workplace discrimination), as well as relevant jurisdictional considerations (e.g., in the United States, the definition of insanity in criminal trials differs from state to state) in order to be able to interact appropriately with judges, attorneys, and other legal professionals. An important aspect of forensic psychology is the ability to testify in court as an expert witness, reformulating psychological findings into the legal language of the courtroom, providing information to legal personnel in a way that can be understood. Further, in order to be a credible witness, the forensic psychologist must understand the philosophy, rules, and standards of the judicial system. Primarily, they must understand the adversarial system. There are also rules about hearsay evidence and most importantly, the exclusionary rule. Lack of a firm grasp of these procedures will result in the forensic psychologist losing credibility in the courtroom. A forensic psychologist can be trained in clinical, social, organizational, or any other branch of psychology.