An ab initio investigation of the quadrupole moment, the polarizability anisotropy and the temperature-independent term entering the electric-field-gradient-induced birefringence (EFGB) of CO2 and CS2 is presented. For the latter property, the results allow us to analyze numerically the differences between two semiclassical theories of the EFGB for nonpolar systems. Accurate electric quadrupole moments are obtained from the combined use of coupled cluster methods and diffusely augmented correlation-consistent basis sets. For CO2, our best ab initio estimate of Theta(0) = (-14.29 +/- 0.09) X 10(-40) Cm-2 is in excellent agreement with the two most recent experimentally deduced results (-14.3 +/- 0.6)X 10-40 Cm-2 and (-14.27 +/- 0.61) X 10(-40) Cm-2.