Ab initio molecular orbital calculations have been carried out for silicate, aluminosilicate, and aluminate clusters to study the NMR characteristics of various types of hydroxyls (OH) that are possibly present in hydrous silicate glasses and melts. The clusters have been optimized with the density functional theory (B3LYP/6-311+G(2df,p)) and their NMR parameters calculated at HF/G-311+G(2df,p). Our calculations suggest that the O-17 and H-2 quadrupolar coupling constants (C-Q(O) and C-Q(H)) and H-1 chemical shift (delta (H)(i)) of SiOH, AlOH, and bridging OH's (Si(OH)Al, Al(OH)Al) all show good correlation with the O-H and O-H . . .O distances. The calculated C-Q(O), C-Q(H), and delta (H)(i) values agree well with those of the experimental data for OH groups with similar O-H . . .O distances in crystalline phases. Hydroxyls with stronger hydrogen bonding tend to yield smaller C-Q(O) and C-Q(H) and larger delta (H)(i). SiOH and bridging OH's of comparable hydrogen-bonding strengths give similar O-17 and H-1 (H-2) NMR parameters. AlOH have a tendency not to form strong Al-O-H . . .O type hydrogen bonding and, thus, give relatively large C-Q(O) and C-Q(H) and small delta (H)(i). On the basis of these calculation results, together with information for hydrogen-bonding strengths estimated from experimental vibrational spectra and H-1 NMR data, we were able to predict O-17 NMR parameters for hydroxyls in hydrous silicate glasses. The observed O-17 NMR peaks for silica gel and hydrous albite glass, that have been attributed to SIGH, are significantly narrower than expected from C-Q(O), suggesting that at least some of the SiOH, if present, must be nonrigid. The observed broad O-17 NMR peaks for hydrous albite and alkali silicate glasses, originally attributed to molecular H2O, could equally well be ascribed to rigid hydroxyls with weak hydrogen bonding.