We have computed the elastic constant tensor forPbZrTiO6,PZT 50/50, in the rhombohedral structure. We find it to be very soft elastically, and the Young’s modulus to be very anisotropic. Our results for PZT are compared with literature values on other oxide perovskites, and the new experimental results on PMN-PT and PZN-PT. The elastic response is an important part of the electromechanical response, and should be studied experimentally and theoretically to help build up a systemic understanding of electromechanical materials. We find that anisotropy in Young’s modulus and elastic softness may be key discriminators in evaluating or improving electromechanical properties. ©2001 American Institute of Physics.