Glutamine (abbreviated as Gln or Q; the abbreviation Glx or Z represents either glutamate or glutamic acid) is one of the 20 amino acids encoded by the standard genetic code. Its side chain is an amide formed by replacing the side-chain hydroxyl of glutamic acid with an amine functional group. It can therefore be considered the amide of the acidic amino acid glutamic acid. Its codons are CAA and CAG.

Glutamine is the most abundant naturally occurring, non-essential amino acid in the human body and one of the only amino acids which directly crosses the blood-brain barrier.[1] In the body it is found circulating in the blood as well as stored in the skeletal muscles. It becomes conditionally essential (requiring intake from food or supplements) in states of illness or injury.

In catabolic states of injury and illness, GLN becomes conditionally-essential (requiring intake from food or supplements). Glutamine has been studied extensively over the past 10-15 years and has been shown to be useful in treatment of serious illnesses, injury, trauma, burns, cancer and its treatment related side-effects as well as in wound healing for postoperative patients.[4][unreliable source?] That is why it is now also classified as a "nutraceutical". Glutamine is also marketed as a supplement used for muscle growth in weightlifting, bodybuilding, endurance and other sports.