The gas phase structures of the [M-H] cations and anions of glycine have been studied by using a combination of ab initio calculations (at the MP2(FC)/6-31+G* level of theory) and tandem mass spectrometry (MS/MS). It was found that the ab initio stability order for the anions is [H 2 NCH 2 CO 2 ] - > [H 2 NCHCO 2 H] - > [HNCH 2 CO 2 H] - . In contrast, the cations exhibit different behaviour, whereas [H 2 NCHCO 2 H] + is predicted to be a stable structure, [H 2 NCH 2 CO 2 ] + spontaneously fragments to the ion-molecule complex [H 2 NCH 2 + ... (OCO)] and the singlet [HNCH 2 CO 2 H] + isomer is predicted to undergo a skeletal rearrangement to form [CH 2 NHCO 2 H] + . MS/MS spectra of [M-H] + cations of various glycine isotopomers were obtained via: (i) collisional activation of electron impact generated cations and (ii) charge reversal of anions formed via HO - negative ion chemical ionization. The resulting spectra were significantly different, suggesting different structures were involved. Neutralization-reionization experiments were performed on [M-H] - anions in order to gain insights into the structures of the intermediate radicals.