The structural development of the Iranian ranges has certain peculiarities which contradict the conventional geosynclinal theory of mountain building. Early orogenic movements resulted in the consolidation of the Precambrian basement and the formation of a vast Iranian platform. Only epeirogenic movements affected the region during the Paleozoic. Precursory Alpine movements in Mesozoic time were strongest in central Iran, although this region and the closely related Alborz (Elburz) mountain area generally retained their epicontinental character, allowing for only a rudimentary geosynclinal development. More clearly geosynclinal conditions developed in peripheral fold belts: the Zagros, the Kopet Dagh, and the east Iranian ranges. Strong folding and thrusting during the Alpine orogeny proper in late Cretaceous-Tertiary time affected most of Iran except the rigid Lut block in the eastern part of the country. The conventional tripartite division of Iran into an extensive median mass and two bordering ranges of geosynclinal origin (Zagros, Alborz) cannot be maintained. The writer replaces this oversimplified interpretation by recognizing the existence of more structural zones which differ in structural development and present tectonic style.