Extensive biological and developmental research over the past 30 years has generated substantial evidence that young children who experience severe deprivation or significant neglect—defined broadly as the ongoing disruption or significant absence of caregiver responsiveness—bear the burdens of a range of adverse consequences. Indeed, deprivation or neglect can cause more harm to a young child’s development than overt physical abuse, including subsequent cognitive delays, impairments in executive functioning, and disruptions of the body’s stress response. This Working Paper from the National Scientific Council on the Developing Child explains why significant deprivation is so harmful in the earliest years of life and why effective interventions are likely to pay significant dividends in better long-term outcomes in learning, health, and parenting of the next generation. http://developingchild.harvard.edu/index.php/resources/reports_and_working_papers/working_papers/wp12/