Abstract
The current understanding of sound properties in glasses is reviewed and compared to that in crystals. Sound damping in oxide glasses is controlled mainly by three processes which in increasing order of the frequency at which they dominate are: the thermal relaxation of defects, relaxation via anharmonic interactions with the thermal bath, and hybridization with optic-like vibrations. The former two also affect distinctly the velocity of sound. The latter one relates to the boson peak and the low temperature plateau generally observed in the thermal conductivity. In addition, in silica and other tetrahedrally coordinated glasses, the sound velocity tends to increase with temperature, presumably owing to a progressive structural change.