Man, with his erect posture, evolves in a world subject to the laws of gravity. His skeleton reflects these constraints. The morphology and static of human spine and biomechanical relationships between spine and pelvis are in direct relation with bipedia. Owing to this position, the pelvis widened and straightened, characteristic sagittal spinal curves appeared and the perispinal muscles were deeply reorganized. Each pelvis is characterized by a major anatomical landmark: the pelvic incidence angle that reflects the sagittal morphology of the pelvis and the position of the sacrum. Based on this anatomical characteristic, a chain of reactions determines the more efficient equilibrium of the whole body in the sagittal plane in term of energy consumption. Incidence affects the sacral slope, which determines lumbar lordosis, which itself influences the pelvic tilt, the thoracic kyphosis, the position of the cervical spine and the head and even the hips and knees' position. All these landmarks can easily be studied on a sagittal whole body radiograph. Knowledge of these functional relationships is essential to understand the origin of sagittal imbalance and above all before surgical treatment of spine disorders, especially when a surgical arthrodesis is considered.Nowadays, digitalized teleradiography remains the most commonly used tool for the study of the body sagittal balance. The irradiation given by this technique is important, and concerns large areas (trunk and pelvis) very sensitive to radiations for often a poor photographic result. Some radiographic tables allow the realization of digitalized spinal radiographs by simultaneous translation of X-ray tube and receptor.EOS system is a new low dose system which gives very good quality images, permits a simultaneous acquisition of upright frontal and sagittal views, is able to cover in the same time the spine and the lower limbs and study the axial plane on 3D envelope reconstructions by bone-morphing technique. This new EOS low dose system take already a great place in the study of the pelvispinal balance and will take a greater one in the future.