Undernutrition is a major cause of morbidity and mortality in emergencies. The response depends on the extent and type of undernutrition in the affected population. Nutritional status is assessed by weight-for-height, mid-upper arm circumference and micronutrient deficiencies. Food aid is distributed in general or selective feeding programmes. Promotion of breastfeeding has been found to be one of the most efficient strategies to prevent undernutrition. There is a lack of evidence to support the optimal composition of food aid products, but there is an increasing focus on the importance of research in this field.