The of immunity of parliament and its Members has led to determine and assure particular privilege in Constitutions or ordinary laws in great majority of countries. This legal institution is to provide freedom of speech and to maintain independence of representatives in exercise of their duties without undue interference or fear. To define and justify of it, different theories like the prestige of representatives' legal personality and doctrine of necessity have been introduced. The legal support, which observes parliamentary privilege, can be generally studied in two categories with distinct descriptions and effects; first, demonstrates benefits and utilization of privilege by representatives before their statements, opinions and votes cast in exercise of their functions, which is idiomatically the principle of nonU€ liability. Second, it supports Members of Parliament (MPs) before legal prosecution, arrest, imprisonment and rest judicial measures, unless by permission and allowance of respective Parliament, because of irrelevant exercises and extralegal parliamentary acts and prevents possibility of immediate prosecution of MPs because of attributed crimes. This kind of immunity, which practically is logical trailer of non - liability principle of representatives before their parliamentary duties, is named the principle of inviolability. The stand of every country in relation to various forms of parliamentary privilege is a little bit different. In certain countries, one of these two forms is accepted and in other countries both of them are accepted to guarantee whole immunity of MPs. The first approach is called solo and second one is called integrative, respectively. In Iran, first approach depended on nonU€liability of representatives because of their statements, has been accepted in Article 86 of Constitution. The accuracy of this acceptance from dynamic Fiqh's (Jurisprudence) point of view is approvable and expediencies and accidental necessities require going along with rest of countries, which accepted principle of parliamentary privilege. Keywords: Parliamentary Privilege, Constitutions and Ordinary Laws, Representatives' Prestige of Legal Personality, Doctrine of Necessity, Principle of Non U€ liability and Principle of Inviolability