Parenteral nutrition practice is a dynamic field where definitive solutions for optimal practice are still evolving. Evidence that early poststress enteral feeding may benefit patient outcome has bolstered the practice axiom: if the gut works, use it. Parenteral nutrition is indicated for the malnourished patient with a nonfunctional small bowel and a long term prognosis. The use of commercially available amino acid solutions for renal failure, hepatic failure, and stress is unresolved. Current research focuses on clinical applications for glutamine, dipeptides, and alternative lipids. Energy prescription emphasizes avoidance of overfeeding. The optimal ratio for non-protein calorie carbohydrate and lipid remains controversial.