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.
Generally, a forensic psychologist is designated as an expert in a specific field of study. The number of areas of expertise in which a forensic psychologist qualifies as an expert increases with experience and reputation. Forensic neuropsychologists are generally asked to appear as expert witnesses in court to discuss cases that involve issues with the brain or brain damage. They may also deal with issues of whether a person is legally competent to stand trial.
Questions asked by the court of a forensic psychologist are generally not questions regarding psychology but are legal questions and the response must be in language the court understands. For example, a forensic psychologist is frequently appointed by the court to assess a defendant's competence to stand trial. The court also frequently appoints a forensic psychologist to assess the state of mind of the defendant at the time of the offense. This is referred to as an evaluation of the defendant's sanity or insanity (which relates to criminal responsibility) at the time of the offense. These are not primarily psychological questions but rather legal ones. Thus, a forensic psychologist must be able to translate psychological information into a legal framework.
Forensic psychologists may be called on to provide sentencing recommendations, treatment recommendations, or any other information the judge requests, such as information regarding mitigating factors, assessment of future risk, and evaluation of witness credibility. Forensic psychology also involves training and evaluating police or other law enforcement personnel, providing law enforcement with criminal profiles, and in other ways working with police departments. Forensic psychologists may work with any party and in criminal or family law. In the United States, they may also help with jury selection.
Forensic psychologists may hold a Ph.D. or Psy.D. in clinical psychology, counseling psychology, social psychology, organizational psychology, or experimental psychology. In order for a psychologist to practice as a forensic psychologist in the United States, it is preferable but not necessary that the individual be a state licensed psychologist and receive certification as a Diplomate in Forensic Psychology by the American Board of Forensic Psychology (although the latter is less important to judges). Ideally, the psychologist would have some years of postdoctoral experience in forensic psychology and have training and supervision in forensic psychology. However, practices vary from state to state and from jurisdiction to jurisdiction. In the United States legal system, the ultimate authority is the judge and the judge may select whomever he or she sees fit to qualify as an expert.
In other countries, training and practitioner requirements vary. In the United Kingdom, for example, a person must obtain the Graduate Basis for Registration with the British Psychological Society—normally through an undergraduate degree. This would be followed by Stages 1 (academic) and 2 (supervised practice) of the Diploma in Forensic Psychology (which would normally take 3 years full-time and 4 years part-time). Assessment occurs via examination, research, supervised practice, and the submission of a portfolio showing expertise across a range of criminological and legal applications of psychology. Once qualified as a "Chartered" psychologist (with a specialism in forensic psychology), a practitioner must engage in Continued Professional Development and demonstrate how much, of what kind, each year, in order to renew his/her practising certificate.