The electron ion collider (EIC) eRHIC at BNL aims at a luminosity of $10^{34}\,{\rm cm}^{-2}{\rm sec}^{-1}$ in collisions of polarized electron and polarized proton, deuteron, and $^3{\rm He}$ beams. We will present an overview of the proposed facility with an emphasis on generation and acceleration of the polarized beams and the expected polarization performance.