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A summary is presented of the major findings of a program whose objective was to investigate the phenomenon of preferential heat generation around damaged regions in composite materials subjected to mechanical vibrations and to develop an understanding of the mechanisms involved in this process. Vibrothermography is a nondestructive inspection technique based upon the utilization of this phenomenon. It has been found that this technique has considerable potential for inspecting composite materials. A significant amount of knowledge has been gained concerning the nature of the heat generation process and the relation of the frequency dependence of the heat patterns to the mechanical excitations. In particular, we how have convincing evidence that the heat generation around a delamination-type defect occurs preferentially at frequencies corresponding to natural resonance modes of anisotropic plates having the size of the delamination and subjected to fixed-fixed boundary conditions.