Psychiatric report is required at the court in several legal statements as well in criminal matters as in civic matters and is subject to the same codes of proofs as any other expert report. Still, psychiatry and its object are absolutely peculiar. The relation that may be kept between the judge and the expert psychiatrist is tinged with many elements of social and professional nature but also of judicial and quibbling nature, simply. While lawyers and legal experts quote that relationship of an usurpation of the judge part by the expert psychiatrist , psychiatrists on the other hand reckon that the expert report is completely perverted by the judicial process. Yet, reality is not univocal. If the psychiatric report is globally a proof among many others, it can still have a crucial impact in the ruling machinery. [*] La présente étude est issue d’un mémoire de maîtrise dirigé par M. le professeur Pierre Noreau. La recherche empirique a été réalisée au printemps 2006 et le mémoire a été présenté à la Faculté des études supérieures de l’Université de Montréal en juin 2006. Il a été classé dans les 10% meilleurs mémoires de la discipline. [**] Courriel : emmanuelle.bernheim@umontreal.ca