With one child in three killed by it, childhood and maternal undernutrition are discussed in a special series of articles in the Lancet. Sarah Maxwell spoke with Zulfiqar Bhutta about his group's massive study, and in particular about the risks of not breastfeeding optimally. The interval from conception to age 24 months has been named as the critical period for child nutrition, with big health effects in adult life. Caroline Fall spoke with Karen Regester about the evidence her group has published in The Lancet on five key studies on maternal and infant nutrition. Simon Cousens talked with Peter Goodwin about a new study of interventions, including promoting breast feeding, and vitamin supplements for combating maternal and child undernutrition. Bruce Cogill gave Peter Goodwin his assessment of the chances of success in the global battle to save the lives of a third of the world's children. Lancet Editor, Richard Horton, explained the importance of these new findings to Sarah Maxwell.