Glutamine is a key amino acid in several metabolic pathways; it’s broadly used as a dietary supplement in physical activity, mainly by its role as essential molecule for energy metabolism and cellular proliferation. Athletes and physical activity practitioners use this amino acid as an ergogenic resource to optimize physical performance and prevent immune impairment. The present study aimed to evaluate the relation between glutamine supplementation and performance in adult subjects with different levels of activity. Indexed databases and public university libraries were searched for relevant works containing the following keywords: “supplement”, “glutamine”, “performance”, “body composition”, “adult men” and “adult women”, limited to works written in English. Inclusion criteria: adult men or woman, strength or endurance training and L-glutamine or glutamine peptide supplementation. Acquired data has demonstrated that glutamine supplementation was able to (1) increase distance and duration of tolerance to intermittent exercise; (2) lower feelings of fatigue; (3) enhance physical and performance measures; (4) optimize the recover from muscle damage and (5) prevent suppression of neutrophil function, especially the production of reactive oxygen species (ROS). Authors also suggest that glutamine supplementation is able to elevate nasal IgA, partially prevent hyperammonemia and apoptosis of human lymphocytes, improve visual reaction time, enhance fluid and electrolyte uptake and further elevate exercise-induced plasma interleukin- 6 (IL-6). Glutamine, however, was unable to improve weightlifting performance, increase salivary immunoglobulin- A (IgA) concentration or elevate plasma levels of glutamine in resting athletes.