An explicit polynomial strain-energy function for tetragonal-orthorhombic-monoclinic zirconia (ZrO2), calibrated from the conventional hydrostatic p−T phase diagram, is used to study the effects of nonhydrostatic loading on the phase equilibria in this material. Several representative sections of the phase diagram of ZrO2 in temperature and stress space, containing both triple and critical points, are computed. A new orthorhombic structure of ZrO2 is predicted to be the most stable phase for a variety of experimentally accessible shear loads, in a wide range of temperatures and pressures.