The authors review recent progress in the design of eRHIC, a proposed high luminosity, polarized electron-ion collider which would make use of the existing RHIC machine. The eRHIC collider aims to provide collisions of electrons and positrons on ions and protons in the center-of-mass energy range of 30-100 GeV, with a luminosity of 10(sup 32)-10(sup 34) cm(sup -2)s(sup -1) for e-p and 10(sup 30)-10(sup 32) cm(sup -2)s(sup -1) for e-Au collisions. An essential design requirement is to provide longitudinally polarized beams of electrons and protons (and, possibly lighter ions) at the collisions point. An eRHIC ZDR has been prepared which considers various aspects of the accelerator design. An electron accelerator, which delivers about 0.5A polarized electron beam current in the electron energy range of 5 to 10 GeV, would be constructed at BNL, near the existing RHIC complex and would intersect an ion ring in at least one of the available ion ring interaction regions. In order to reach the luminosity goals, some upgrades in the ion rings would also be required.