The Relativistic Heavy Ion Collider at Brookhaven will extend the present heavy ion capabilities of the AGS into an energy domain not available at any other laboratory within the foreseeable future. Operation of the AGS for heavy ion experiments started in October 1986 with the delivery of O/sup 8 +/ beams. Subsequently, the mass range was extended with the AGS delivering typically 2 x 108 Si/sup 14 +/ ions/pulse at a kinetic energy of 13.8 GeV/u. Completion of the AGS booster synchrotron in 1991 will extend the mass range to the heaviest ions, typically 179Au, with 238U a definite possibility. The acceleration of heavy ions to very high energies at Brookhaven was already considered for the ISABELLE/CBA project. After its cancellation, the realization of a dedicated heavy ion collider in the vacant tunnel became feasible and the design objectives were defined in 1983 by a Task Force on Relativistic Heavy Ion Physics. The study of such a heavy ion accelerator/collider was initially supported by generic RandD funds and later on as part of the Brookhaven Exploratory Research Program. The results of this multi-year RandD effort were presented in the May 1986 Conceptual Design Report (CDR). This document remains valid in most respects but progress resulting from two years of intensive RandD work, now supported with direct DOE funds, in the areas of accelerator physics and superconducting magnet technology resulted in a few design improvements. The present paper summarizes the major features of the RHIC design with emphasis on those aspects of particular interest to the future user and it concludes with a short discussion of the superconducting magnet RandD program. 10 refs., 15 figs., 3 tabs.