Neglect is the most common form of child abuse. It can also have the most serious impact on a child's development, with an increased and accompanying risk of the emergence of psychiatric disorders from adolescence to adulthood. Child neglect is under-recognized today, due to a lack of training for professionals, the orientation of child psychiatry, and difficulties in understanding what this vague concept refers to. After proposing definitions of neglect, its characteristics, and its effects, we present the possible actions of the child psychiatrist in the ecosystem of the neglected child. Neglect is neither a legal nor a medical term. It is, however, used by doctors and social workers, with a loose definition as the absence of appropriate care for a child's development. Neglect is multifactorial. The French consensus approach to the basic needs of the child has highlighted a meta-need for security, emphasizing attachment and the particular qualities of the caregiver. In light of this report, we understand that affective or emotional neglect is the most problematic form of neglect. The effects of neglect are early, depending on the child's age. They can manifest as developmental delays, sleep disorders, tonus disorders in infants, intellectual disorders, and various internalized and externalized disorders in adolescence. Mortality and morbidity are increased in cases of neglect, and developmental sequelae have been described. Neglect has a greater impact on development than physical abuse. The child psychiatrist can take three types of action to treat the neglected child. Firstly, he or she must identify neglect and alert the appropriate instances so as to protect the child. Identification involves being aware of indicators of neglect and a particular clinical pattern that varies according to age, requiring the exploration of the different lines of development. Three clinical patterns seem to be linked to extreme neglect: anaclitic depression, post-traumatic stress disorder, particularly complex developmental trauma, and attachment disorders. When faced with symptoms suggestive of neglect, the child psychiatrist should try to rule out a sensory or neurodevelopmental cause, sometimes seeking the advice of a specialist. He or she will observe the child's behavior alone and with his or her parents, as well as parent-child relationships, and will consider the child outside the family microsystem in an ecosystemic approach. The child psychiatrist can use available standardized tools that explore the various dimensions of neglect. This multi-consultation assessment should not delay the child psychiatrist's initial actions, given the narrow developmental windows. In particular, the child psychiatrist may be required to report the child's situation to the administrative and judicial authorities. The care provided to the neglected child will then take place within the child's own ecosystem. Interventions must be early, participative and in partnership with social services, educators, and staff at the placement site. Care will seek to compensate for the negative developmental effects of neglect, in order to correct the child's developmental trajectory. It must take into account the child's psychopathology. Psychotherapy, the framework of which will need to be adapted, will help the child to assume ownership of his or her history. Child psychiatrists can also take part in innovative initiatives to help children at risk, such as mobile teams. The final action to be developed by the trained child psychiatrist is preventative. It is important that child psychiatrists be informed and trained to deal with neglect and its effects. Today's neglected children will be tomorrow's adults with the most psychiatric disorders.