This review focuses on the vibrational spectra of icy solids, in particular ice I, and the value of the spectra in monitoring point defect activity within the various hydrogen-bonded networks. After a brief review of the spectra of icy substances containing only H2O or D2O, an attempt is made to update both the spectroscopic data and the interpretation by emphasizing recent results for isotopically diluted/decoupled D2O in H2O ice I, amorphous ice and the clathrate hydrates. These data are informative of the magnitude of the intramolecular and intermolecular O-H oscillator coupling strengths, the strength of the Fermi interaction between v1and 2v2, the influence of symmetric hydrogen bonding on the directionality of the water-molecule bond-dipole-moment derivative, and, perhaps most importantly, the spatial extent of the collective vibrations in icy substances. The interpretation of the spectra retains, and expands, the assignment of Whalley (1977) based on the view that intermolecular coupling forces, caused by hydrogen bonding (v1) and the polarization field (v3), give rise to collective oscillations that dominate the appearance of the infrared and Raman stretching-mode band complexes.