Seismic attenuation (1/Q) changes abruptly between the stable Eurasian craton and adjacent mountain belts associated with the Alpine-Himalayan collision. New attenuation measurements on local body and coda waves provide quantitative constraints on this contrast, near the Caucasus, Kopet Dagh, and Tien Shan mountains. The 1/Q estimates from all range fronts are similar, the mountains being two to three times more attenuative than adjacent stable platforms. These 1/Q variations are a reasonable proxy for temperature variations, and reveal crustal heating on the order of 100 °C but probably not melting beneath the mountain ranges. Attenuation (1/Q) is high wherever high topography is seen, implying that active mountains are typically hot. Hence, processes that generate or transport heat dominate advective cooling due to lithospheric thickening, even over the 10–20 m.y. lifetimes of these young mountain belts.