Physics   The nuclear physics community worldwide has suggested that a high-luminosity, at or above 1033 cm-2sec-1, polarized Electron-Ion Collider with variable center-of-mass range ?s in the range of 20 to 100 GeV would allow us to probe the hadronic structure of matter and provide answers to these questions. The 2001 Long Range Plan for the next decade, outlining opportunities in nuclear science, put an Electron-Ion Collider forward as the next major facility to consider for the field. They emphasized the need to refine the scientific case, and to pursue the accelerator R&D necessary to ensure that the optimum technical design could be chosen. The 2002 Ad-hoc Facilities NSAC Subcommittee identified the research program of such a facility as “absolutely central to Nuclear Physics”. Facility   ELIC is an electron-ion collider with center of mass energy of 20 to 90 GeV and luminosity up to 8x1034 cm-2s-1. This high luminosity collider is envisioned as a future upgrade of CEBAF, beyond the 12 GeV Upgrade, and compatible with simultaneous operation of the 12 GeV CEBAF (or a potential extension to 24 GeV) for fixed-target experiments. The CEBAF accelerator with polarized injector can be used as a full energy injector into a 3-9 GeV electron storage ring. A positron source is envisioned as an addition to the CEBAF injector, for generating positrons that can be accelerated in CEBAF, accumulated and polarized in the electron storage ring, and collide with ions with luminosity similar to the electron/ion collisions. The ELIC facility is designed to produce a variety of polarized light ion species: p, d, 3He and Li, and unpolarized ion species. To attain the required ion beams, an ion facility must be constructed, a major component of which is a 225 GeV collider ring located in the same tunnel and below the electron storage ring. A critical component of the ion complex is an ERL-based continuous electron cooling facility, anticipated to provide low emittance and simultaneously very short ion bunches. ELIC is designed to accommodate up to four interaction regions (IR’s), consistent with realistic detector designs. Longitudinal polarization is guaranteed for protons, electrons, and positrons in all four IR’s simultaneously and for deuterons in up to two IR’s simultaneously. An alternate design approach for ELIC is based on the linac-ring concept, in which CEBAF operates as a single-pass Energy Recovery Linac (ERL) providing full energy electrons for collisions with the ions. Although this approach promises potentially higher luminosity than the ring-ring option, it requires significant technological advances and associated R&D. A linac-ring ELIC design is an ultimate Upgrade of ELIC, fully compatible with and a natural extension of the ring-ring scheme.