The dielectric properties of condensed matter do not in general follow the Debye model so that, to account for the actual behaviour in solids, distributions of relaxation times have been postulated. It is shown that the frequency response of all solids has common features which can be generalized to give a correct picture of the experimental situation. A recently developed approach to relaxation processes that involves cooperative interactions is outlined and shown to contain the generalized behaviour observed and to give a new approach to the understanding of the cooperative interactions that occur in solids.