ITER is an unprecedented global partnership to demonstrate the scientific and technological feasibility of generating carbon-free, and virtually unlimited, energy through the fusion of hydrogen isotopes. Now under construction in southern France, the ITER fusion reactor is designed to achieve and sustain self-heated, or “burning,” plasma that can produce ten times more power than required for plasma heating. This overview provides an introduction to fusion, summarizes the history of the ITER project, describes key subsystems and elements of the ITER reactor, and includes objectives and goals of the ITER research plan.