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Tectonic deformation of blocks neighboring fault zones has been thought to aid in accommodating regional displacements. In general, these block-bounding faults possess continuous geometry and similar kinematics. However, the northwestern boundary of the Tianshan Mountains (NWBTS) involves two groups of faults that strike NW and NE. GPS velocities show that contemporary deformation takes place in a zone of 300 km wide in the NWBTS and is roughly dominated by left-lateral shear. Left-lateral shear motion of ∼5–6 mm/yr along the NWBTS is accommodated by right-lateral slip and counterclockwise rotation of fault wallrocks on the NW-striking faults and left-lateral faulting on the NE-striking faults. Present-day deformation associated with the ongoing India-Eurasia collision in the NWBTS is best described as the opposite sense of strike-slip faulting and crustal rotation. The difference in lithospheric strengthening between the Kazakh Platform and Tianshan deflects strain toward the northeast and drives the dynamic process in this region.