The deformation of the lithosphere in western Himalaya and Karakoram is analyzed by correlating Bouguer gravity anomalies and topographic heights sampled along profiles in the direction of the Indo-Asian collision. The spectral features of the coherence, linear admittance, and correlation coefficients between topography and deformation at depth support the hypothesis that the flexural mode of lithospheric deformation is complemented by a folding mode, with typical wavelengths concentrated in bands centered at 250 and 120 km. When combined with realistic models of a rheologically stratified lithosphere with two strong layers (upper crust and upper mantle) sandwiching a weak, very ductile layer (the lower crust), the data are consistent with a model of response to horizontal deformation in which a coupled, biharmonic folding instability develops: The lithosphere as a whole warps with the longer wavelengths and the upper layer alone also with the shorter wavelengths. Major faults, such as the Main Boundary Thrust, or the Main Karakoram Thrust and the computed folds of the upper layer are phased, as if there were a causal relationship between the position of the faults and the zones of highest strain in the crust. ¿ 2000 American Geophysical Union