Glycine, NH₂CH₂COOH, is the simplest amino acid. It is colorless, crystalline, water soluble, and amphoteric because it has both the amine group (-NH₂, basic) and the carboxylate group (-COOH, acidic). In acidic solutions it behaves as a base to form the ⁺H₃NCH₂COOH ion; in basic solutions it acts as an acid to form the H₂NCH₂COO^- ion. In neutral solutions, the ion ⁺H₃NCH₂COO^- can exist .

Glycine is a common residue in proteins, especially collagen and elastin and is not optically active. It is also a major inhibitory neurotransmitter in the spinal cord and brainstem of the vertebrate central nervous system.