The ITER design activities are now focused on the development ofa design for a tokamak burning plasma experiment which willachieve Q = 10 in long-pulse, inductively driven plasmas andwhich aims to demonstrate steady-state operation at Q = 5 usingnon-inductive current drive. The device is designed to allowoperational flexibility in plasma equilibrium and operatingscenarios, and it is intended that the possibility of ignitedoperation under favourable plasma scenarios should not beexcluded. A final design and parameter set has not yet beenselected, but considerable progress has been made in developing aseries of candidate designs which allow the critical physics andengineering issues to be explored. Here the physics underlying thedesign options and performance projections, as well as thephysics issues to be addressed in the proposed experiment, areanalysed.