The author here develops his concepts now known as the symbiotic phase of the infant with her mother and then the individualisation-separation stage. It describes the psychological and physical development since birth, ranging from a short autistic phase to that of symbiosis, where a mther-child symbiotic dyade dominates, to those of successive stages of individualisation marked by the more or less well integrated experiences of separation. Starting from the clinic of two children, she highlighted the sensitivity of these periods to the onset of trauma and to the degree of receptiveness of the maternal and family environment, for the genuine creation of identity and personality.