This book contains the proceedings of a workshop held at the Institute Laue-Langevin in Grenoble in September 1988. Review articles and contributed papers survey recent theoretical and experimental developments on disordered materials and in particular on glasses. A large part of the book concerns the recently proposed mode-coupling approach to the behaviour of a viscous liquid around its glass transition, where the relevant dynamics extend over a broad range in time scales and the application of quite different experimental techniques becomes essential. Contributions report on experiments using dielectric relaxation, NMR or light scattering techniques, and especially neutron scattering techniques. One signature of disordered materials is the occurrence of an excess vibrational density of states at low frequencies. Some situations are presented where the density of states can be understood by taking into account the peculiarities of intra- and intermolecular motions. Another approach to the dynamics of disordered materials is the fracton picture, developed to describe the excitations of fractal objects. Several contributions discuss the dynamics of such fractals, studying mainly the vibrational density of states, and some discuss the application of the fracton concept to materials without a fractal structure like glasses.