This chapter discusses a number of key issues: the importance of nutritional support, both enteral (oral nutritional supplements, enteral tube feeding) and parenteral nutrition in the treatment of the nutritionally compromised patient with gastrointestinal and liver disease; prescribing and monitoring nutritional support; refeeding syndrome; practicalities, indications and contraindications and complications of using enteral and parenteral nutrition; choosing feeds with an optimal nutrient composition for nutritional support, including specific feeds for disease states; the evidence base for using nutritional support in the patient with gastrointestinal and liver disease.