The prevalence of childhood obesity has increased rapidly over the past two decades. Excess weight in childhood tracks into adult life and causes problems both in the short term and in the long term. National surveys show that more than one in five children are already overweight (13%) or obese (10%) when they start school. Hence any efforts to prevent obesity must start early. The Foresight Report and the Healthy Weight Healthy Lives strategy have highlighted the importance of preventing childhood obesity by focussing on the early years. However, to date there is little evidence on which to develop effective preventive strategies. Infancy is a period of rapid growth and weight gain and obesity prevention during this period may be effective. Nutrition and growth during infancy may also have long term effects by altering eating behaviours and risks of obesity and obesity-related disorders in later life. UK Infant Feeding Surveys show that at birth one in three (35%) of babies receive formula-milk and this number increases to almost all babies (92%) at 6 months of age. Hence, in addition to promoting breastfeeding, it important to optimise the growth of formula-milk fed babies. Our previous research shows that parents who give their babies formula-milk as part of their everyday diet need more information and support. Researchers at the Centre for Diet and Activity Research (CEDAR) and MRC Epidemiology Unit in Cambridge have been working with mothers and healthcare professionals to develop a feeding programme which aims to avoid excess weight gain in formula-milk fed babies. The programme we have developed aims to support parents who feed their babies formula-milk to achieve a healthy pattern of growth and weight gain. The infant feeding programme will be tested in a randomised controlled trial involving 700 mothers and their babies. Half the mothers will be given advice and support to follow the new feeding programme. The other half will be given routine advice about formula-milk feeding and weaning. The growth of babies in the two groups will be compared. This comparison is important to test whether our new feeding programme is effective in preventing excess weight gain and subsequent obesity. The results of the study will help to inform infant feeding guidelines and will also help us understand the links between infant feeding, behaviour, appetite and growth.