Despite the increasing obesity of the American population, many chronically ill patients are malnourished. When this malnutrition is combined with the hypermetabolic response and protein catabolism of an acute event, such as an operation, nutritional support becomes an important facet for optimal critical care. This chapter reviews the basic tenants of nutritional support with special emphasis on patients with pulmonary compromise. Important aspects of caloric and protein support are discussed and enteral nutrition is emphasized because of its numerous advantages and documented improvement in outcome.