A least squares procedure is used to extract pure path Tibetan group velocities in the period range 8--100 s from fundamental mode Rayleigh and Love waves recorded along 50 mixed paths. The crustal model derived from these dispersion data reveals that the lower half of the very thick (74¿10 km) Tibetan crust has a shear velocity similar to those found in the lower crust beneath stable continental and shield regions. A second interesting feature of the model is the presence of a prominent low-velocity channel at midcrustal depth. The uniqueness of the Tibetan crustal structure places the plateau region in a class by itself among tectonic provinces characterized by high heat flow and/or wide spread recent volcanism, setting stringent constraints on tectonic models of the Tibetan Plateau.