The article analyzes the main assumptions of Iran's "mosaic defence", the implementation of which followed the US invasion of Afghanistan and Iraq. The introduction of a unique model of defence by Iran was a response to the changes that took place as a result of the American intervention in the Middle East and the resulting threats to Iran's security. One of the elements of the "mosaic defence" system (defa e mozaik), which exceeds the borders of Iran, is the The Organization for Mobilization of the Oppressed – Basij. This unique military structure stems from both the Iranian Constitution and Iran's approach to war, which have been shaped as much by historical experience as by religious ideology. During the study special attention was paid to The Organization for Mobilization of the Oppressed - Basij, which is one of the main pillars of Iran's defence in the event of armed aggression, armed conflict and internal threats. As the "mosaic defence" strategy includes hybrid and asymmetric activities, other elements of the system, also from outside Iran, were identified. The basis for the research is the Constitution of the Islamic Republic of Iran, the Constitution of the Army of the Guardians of the Revolution, the Act regulating the employment in the Army of Revolutionary Guards and the analysis of reports prepared by RAND Corporation and other credible research centers and institutions dealing with security issues in the Middle East. The study answers the questions concerning the main determinants of the adopted model of "mosaic defence" and its main elements, the structure of The Organization for Mobilization of the Oppressed and its role in defending the Islamic regime.