Among the many political systems in the Middle East, the regime in the Islamic Republic of Iran stands out as one of the most peculiar. There, the formal government--president, parliament, and other official governing components-- is paralleled by more powerful revolutionary institutions that help shape regime policy. But a third influential stand in Irans volatile political dynamic is more unfamiliar to many, namely, the vigilante groups used by hard-liners to intimidate reformers with raw violence. In this Washington Institute Policy Paper, historian Michael Rubin presents an incisive and comprehensive survey of Iran's vigilantes, or " pressure groups, " along with an exploration of the deep roots these groups have in modern Iranian history. Drawing on both a wide array of Persian language sources and his own research conducted in Iran, Dr. Rubin concludes that--despite the inevitability of political change suggested by demographic and economic realities in the Khatami era--the prospects for real reform in Iran within the existing system of rule are weakened by vigilante activism. The strategic use of vigilantes to frustrate reform also raises important policy issues for the U.S. government. The United States, Dr. Rubin argues should not tolerate a shell game in which vigilantes--sponsored by those in power--carry out hostile actions for which the regime then conveniently denies responsibility. If the Iranian president cannot effectively suppress the vigilante groups, then he may be too weak a figure to implement meaningful changes in foreign or domestic policy. Understanding the threat these vigilante groups pose can only improve America's ability to formulate effectivepolicy toward Iran. This valuable Policy Paper, incredibly rich in detail, brings vital scholarship to bear on that understanding.