The MHD stability limits to the operational space for the International Thermonuclear Experimental Reactor (ITER) have been examined with the PEST ideal stability code. Constraints on ITER operation have been examined for the nominal operating scenarios and for possible design variants. Rather than relying on evaluation of a relatively small number of sample cases, the approach has been to construct an approximation to the overall operational space and to compare this with the observed limits in high-β tokamaks. An extensive database with ∼20,000 stability results has been compiled for use by the ITER design team. Results from these studies show that the design values of the Troyon factor (g ∼ 2.5 for ignition studies and g ∼ 3 for the technology phase), which are based on present experiments, are also expected to be attainable for ITER conditions, for which the configuration and wall-stabilization environment differ from those in present experiments. Strongly peaked pressure profiles lead to degraded high-β performance. Values of g ∼ 4 are found for higher safety factor (qψ ≥ 4) than that of the present design (qψ ∼ 3). Profiles with q(0) < 1 are shown to give g ∼ 2.5, if the current density profile provides optimum shear. The overall operational spaces are presented for g-qψ, qψ-li, q-αp, and li-qψ.