The Iranian Plateau and the south Caspian basin are caught in the collision zone between Eurasia and Arabia and as a result are actively deforming. The current deformation is apparent in geodesy. The record of prior deformation is contained in the complex crustal structure of the region. We invert teleseismic receiver functions from seismographs located in the Iranian Plateau and the south Caspian basin to explore this variations in crustal structure. Data for this study comes from two sources: the permanent broadband seismic network of the International Institute for Earthquake Engineering and Seismology in Iran and temporary broadband seismograph stations operated by the University of Cambridge in Azerbaijan and southern Turkmenistan. In southern Turkmenistan along the frontal fault of the Kopet Dagh Mountains the crust is 45-50 km thick.Southwards into the Turkmenian Lowlands which is structurally part of the south Caspian Basin, the crust thins to about 30km thick and consist of 11 km of sediment overlying the crystalline basement. There are few data for the Alborz Mountain but those which do exist suggest that the crust is about 35 km thick and that the range has not pronounced crustal root. The crust is 46km thick beneath the Zagros Mountains where the continent-continent collision is most recent and clear, similar to the crustal thickness in central Iran.