This document discusses addressing the underlying and basic causes of child undernutrition in developing countries. It analyzes available evidence on effective interventions that work to reduce undernutrition through both "short route" interventions like increasing micronutrient intake as well as "long route" interventions that address underlying causes like improving household food production and women's status. It finds that multisectoral approaches targeting multiple causes are most effective at reducing undernutrition. However, challenges remain in scaling up interventions. Cost-effectiveness analysis shows nutrition programs provide high economic returns, but more investment is still needed to combat undernutrition.