Obesity and nutrition-related chronic disorders are fast rising in developing countries. But undernutrition - stunting, underweight, wasting and micronutrient deficiences - still affect millions of preschool children in both rural and urban settings increasing the risks of morbidity and mortality, impairing cognitve development, reducing productivity and increasing the risk of chronic diseases in later life. In addition undernutrition has a transgenerational effect. Here I review the evidence for a synergistic effect of inadequate nutrition (breastfeeding, complementary feeding), infection, and inappropriate mother-child interactions on growth and nutritional deficiencies. Underlying socioeconomic, environmental and genetic factors are also explored. Finally some perspectives on how urbanization and globalization may affect the prevalence and distribution of undernutrition are discussed. Fighting child under-nutrition is still an urgent necessity and a moral imperative. Copyright (C) 2009 Nestec Ltd., Vevey/S. Karger AG, Basel