The radiotherapy of the breast or the chest wall is a complex technique. The definition of the gross tumour volume and the clinical target volume depends on clinical, anatomical and histological criteria. The volumes are located by physical examination, mammography, echography and tomodensitometry. The implantation of surgical clips in the lumpectomy cavity is useful for the boost field. The planning target volume takes into consideration movements of tissues during respiration and variations in beam geometry characteristics. The organs at risk (heart, lung) must be considered systematically. Technical contrivances are necessary to modify and homogenize dose distribution. Conformational irradiation allows an individually design treatment planning. Intensity-modulated radiotherapy technique is a future advantageous technique still under evaluation.