Malnutrition associated with critical illness has been unequivocally associated with increased morbidity and mortality in humans. Because malnutrition may similarly affect veterinary patients, the nutritional requirements of hospitalized critically ill animals must be properly addressed. Proper nutritional support is increasingly being recognized as an important therapeutic intervention in the care of critically ill patients. The current focus of veterinary critical care nutrition, and the major focus of this article, is on carefully selecting the patients most likely to benefit from nutritional support, deciding when to intervene, and optimizing nutritional support to individual patients.