One of the moral rights related to the personality of individuals is the right to fame. Legal systems have supported this right in different ways. One of these methods is applying the rules governing tortious liability and imposing compensation on the violators of this right. Based on this, in the American and English legal systems, they have used the format and title of "defamation". The question is what are the concept, basis, conditions and pillars of defamation? What types of defenses are recognized in these two legal systems? And is it possible to file tortious liability lawsuits due to defamation in Iranian law? The basis of this responsibility in English law is strict liability, and in American and Iranian law, it is based on fault. Also, its elements are: existence of defamatory statements, publication of statements, attribution to the victim and loss. In addition, the consent of the petitioner, the public interest, etc. are among the defamation defenses and factors that create a balance between the right to freedom of expression and the right to reputation in American and British law, which seems that only the public interest can be accepted as a defense in Iranian law. The mission of this article is to achieve the rules governing tortious liability caused by defamation in Iranian law with an analytical-descriptive approach and with a comparative look at the American and English legal systems.