Using our Stark-modulated free-expansion jet spectrometer, we have measured and subsequently analyzed the rotational spectra of the two C-13, the N-15 and the methylene-d(2) isotopomers of the amino acid glycine conformers 1 and 2 and of the N,O-d(3) isotopomer for conformer 2. The structural implications of the derived rotational constants, in light of published geometric parameters from elaborate post-Hartree-Fock ab initio calculations, have led to the conclusion that both of these conformers have r(p) structures of C-s symmetry. A twisted C-1 symmetry modification of conformer 2, designated 3, is the favored prediction of elaborate ab initio calculations, but the effect of the zero-point twisting vibration would give either conformation an rp geometry of C, symmetry. Thus there is no discrepancy between theory and experiment. From a sensitive survey scan of the spectrum of the main isotopomer, an upper limit of 1/5 has been set for the abundance of the theoretical conformer 4 relative to 2. This result appears to be in conflict with the most elaborate nb initio calculations, which give 4 as energetically similar to 2 and may point to the importance of conformational relaxation during the jet expansion for higher energy conformers that have suitably low barriers to isomerization.