The high flux of equivalent photons present in relativistic heavy ion collisions of two chargesZ 1 andZ 2 gives rise to the collision of two equivalent photons. The cross-sections for various processes are directly related to the correspondingγ- γ cross-sections. As compared toγ- γ physics being studied at e+ e− colliders, we find that high energy states will not be so easily accessible at the existing facilities, however, the enhancement factor (Z 1 Z 2)2 in the expression for the cross section will provide very large photon fluxes for lower energies.