Undernutrition represents a wide-spread clinical state in outpatients and inpatients. It is associated with a high morbidity and mortality, an impaired quality of life, and increased healthcare costs. Early diagnosis and treatement help to reduce these medical and economic consequences. Oral nutritive supplements (ONS) are simple, effective and economic medical treatments to fight against undernutrition. However, they are insufficiently used for outpatients because of lack of knowledge. This article reviews the impact of ONS, their indications and contraindications and their modalities of prescription and focuses especially on community-dwelling patients.