The ITER facility while a major extension of the scientific and technical accomplishments of the worldwide fusion program is based on an extensive set of research and technical data. Recent experimental results, which affect the design, will be reviewed. ITER will address key scientific issues critical to magnetic fusion development. The confinement and stability of plasmas capable of achieving large values of fusion power and hence alpha heating will be the first goal. The subsequent achievement of high values of fusion power relative to the heating power will enable the study of the physics of burning plasmas in regimes, which were not accessible previously in JET and TFTR. Not only will the self-heating of the plasma be studied in regimes where the self-heating is dominant but also the effect of large populations of energetic alpha particles on plasma stability will be assessed. The understanding of the physics of burning plasma will also be applicable to other toroidal configurations. ITER will resolve key questions regarding the ability to achieve and control burning plasmas.