On some occasions the linguist is asked to provide investigative assistance or expert evidence for use in Court. Within the linguistics literature there has been considerable focus on the rules for admission of authorship identification evidence to criminal prosecutions, but the role of the linguist in providing evidence is broader than this. Much of the evidence provided by linguists does not involve authorship identification, and the assistance a linguist may offer is not restricted to only providing evidence for criminal prosecution. Investigative linguists can be considered that portion of forensic linguistics which provides advice and opinions for investigative and evidential purposes.