A unit cell of a layer crystal may contain several layers and the atoms in these layers may interact with one another in different ways. The dependences of the forces of the interaction between the atoms on the distances separating them are also different. The deformation effects in crystals of this kind are unusual. This review reports experimental results obtained in studies of vibrational and electronic spectra of graphite and of layer semiconductors (mainly III--VI compounds) under conditions of elastic deformation at various temperatures. An analysis is made of the results of experimental investigations of thermal expansion of layer crystals. In each case a discussion is given of models which, on the whole, can provide a satisfactory explanation of the nature of the characteristic features of the observed effects.