Enteral nutrition is an integrated part of the therapy in several diseases and clinical conditions. It is used to improve the clinical course and prognosis of patients with inadequate oral nutritional intake or with malnutrition. In addition, enteral nutrition may act in modulating the metabolic state of patients. Enteral diets are industrially made and have a defined composition and consistency. Enteral nutrition is provided as an oral supplement, via nasogastric/nasointestinal tubes or via gastro- or enterostomy, and requires a well functioning intestinal tract. Enteral nutrition is frequently used supplementary to oral or parenteral nutrition. In most patients standard diets can be used. Diet modifications include the energy density, the relation of carbohydrates, fat and nitrogen source and the content of specific nutrients, i. e. specific amino acids, nucleotides or fatty acids to improve the immune function. These modified diets are used for specific indications which are highlighted in this article.