One of the most definitive concepts of child development specifies that prolonged deprivation of maternal care affects adversely the personality development of children. Many studies in Britain and the United States during the past fifty years have produced evidence of various kinds to demonstrate the particular harm that may come to infants who are institutionalized, or whose care in other settings has similarly been defective in mothering, especially when this has been distinguished by discontinuity, insufficiency, or distortion. Bowlby's monograph on maternal care and mental health published by the World Health Organization in 1951 was not only an exhaustive review of world literature and a summary of his own studies, but included theories about the influence of maternal deprivation on the child's personality. Bowlby's indictment of nurseries and other institutions, particularly hospitals, had a widespread and dramatic influence on improving the care of children in institutions. Moreover, his work has stimulated in the past ten years much research aimed at clarifying the issues and providing new evidence in support of Bowlby's thesis or in contradiction of it.