Glutamic acid or glutamate is one of the 20 most common natural amino acids. As its name indicates, it is acidic, with a carboxylic acid component to its side chain.

Glutamic acid is critical for proper cell function, but it is not considered an essential nutrient in humans because the body can manufacture it from simpler compounds.

In addition to being one of the building blocks in protein synthesis, it is the most widespread neurotransmitter in brain function, as an excitatory neurotransmitter and as a precursor for the synthesis of GABA in GABAergic neurons. Glutamate activates both ionotropic and metabotropic glutamate receptors. The ionotropic ones being non-NMDA (AMPA and kainate ) and NMDA receptors. Free glutamic acid cannot cross the blood-brain barrier in appreciable quantities; instead it is converted into L-glutamine, which the brain uses for fuel and protein synthesis.

It is conjectured that glutamate is involved in cognitive functions like learning and memory in the brain, though excessive amounts may cause neuronal damage associated in diseases like amyotrophic lateral sclerosis, lathyrism, and Alzheimer's disease. Also, the drug phencyclidine (more commonly known as PCP) antagonizes glutamate at the NMDA receptor, causing behavior reminiscent of schizophrenia.

The sodium salt of glutamic acid, monosodium glutamate (MSG) is responsible for one of the five basic tastes of the human sense of taste (umami), and MSG is extensively used as a food additive.