The eRHIC project plans to expand Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) with a high-intensity electron beam. Building on the exciting discoveries of RHIC, CERN, HERA and others, eRHIC will break new ground in collider luminosity and will push the frontiers of knowledge in nucleon and nuclear structure and in spin physics. The varied eRHIC physics programme and the proposed machine design will be presented and discussed.