The programmatic objective of the International Thermonuclear Experimental Reactor (ITER) calls for it to demonstrate controlled ignition and extended burn of deuterium-tritium plasmas, to demonstrate essential fusion reactor technologies in an integrated system, and to perform integrated testing of high-heat flux and nuclear components. The ITER design, as embodied in the Final Design Report, and its physics basis are presented and the projections of plasma performance are summarized together with the assessment of ITER's engineering feasibility and of the progress in validating technology R&D. The future prospects for ITER and its potential central role as an integrated physics and engineering experiment in the overall development of controlled fusion as a source of useful energy are discussed.