Malnutrition – specifically undernutrition – is a state in which a deficiency of energy, protein and other nutrients causes adverse effects on the body, its function and clinical outcomes. Malnutrition can be disease-related or caused by social factors; the two are often inter-related. More than 3 million people in the UK are malnourished or ‘at risk’ of malnutrition, 93% of whom reside in the community. It commonly affects older people and those with certain medical conditions. With a pivotal role in providing care in secondary and community settings, prescribers are increasingly involved in quality improvement programmes to manage malnutrition, including the appropriate use of oral nutritional supplements. This article seeks to improve understanding of the impact of malnutrition on individuals and the wider healthcare economy, identification of those at risk and the effective use of oral nutrition support.