The ITER physics group has been responsible for developing the physics guidelines and physics design requirements for ITER, the design of the diagnostic systems and the development and coordination of the ITER Physics R and D Program. These requirements have been based on tokamak experimental data and credible extrapolations of that data. Assessment of the energy confinement and MHD stability requirements led to the choice of the major plasma parameters of 22 MA for the plasma current, a toroidal field of ~ 5 T, aspect ratio of ~ 3 and an elongation of ~ 2. Among the major accomplishments of the physics group has been the development of a database and an empirical scaling for L-mode energy confinement and the facilitation of an H-mode database and scaling. The divertor heat loads have been estimated by using experimentally validated models. The thermal and mechanical loads due to off- normal events such as disruptions have been based on analysis of the data from tokamaks such as TFTR, JET, JT-60, DIII-D, and TORE-Supra. To achieve the required availability of 10%, the pulse length has been extended by the use of current drive using 75 MW 1.3 MeV neutral beam and 45 MW Lower Hybrid systems. Plasma shaping and control of the high beta, elongated plasma is provided by seven pairs of poloidal field coils located exterior to the toroidal field coils. A relatively complete set of plasma diagnostics is planned for ITER. Finally, a Physics R and D program has been developed to ensure that the international fusion program will address the issues which either introduce uncertainties into the design or lead to demanding design requirements.