The Inha System—which can be translated as the intelligence service, the news agency, or even the espionage service—was adopted by the governments during the Persian Middle Period as a strategy to maintain internal security. Governments, in this period, were forced to create their intelligence services in the forms of such institutions as the Courier System, the Controllership Bureau, and the Inha System in order to properly manage the extensive realm of government by means of collecting news and information from every corner of the country by training a number of spies called Monhees. Dealing with information, intelligence, and domestic security, such institutions were regarded as the “eyes and ears” of governments throughout the territory because of their inspection, controlling, and espionage services. The present study tries to explain the concepts of Inha and Monhee and analyze the functions of this intelligence institution in espionage activities and its role in the stability of central governments during the middle period of Iran’s history in a descriptive-analytical manner. Findings of the present study show that the Intelligence Service had a high status in the governmental system since the proper functioning, or else the incompetence, of espionage-intelligence organizations could determine the survival or the extinction of a political power.