Glutamine is an amino acid that is used for many important processes in the body. Products of its metabolism are key substrates for many cell and organ functions. Glutamine appears to become a conditionally essential amino acid during times of metabolic stress, and it is used at a high rate by immune cells and gut mucosal cells. Studies have investigated whether supplemental enteral glutamine improves clinical outcomes in critically ill patients; however, there is a lack of clear evidence. Currently it is only recommended that enteral glutamine supplementation be considered for critically ill burn and trauma patients.