A new theory of the self-ignition of coal was developed, based on the principle of the spontaneous disintegration of coal resulting from the effect of potential energy, which is accumulated in the coal and causes mechanical stress. This leads to the formation of microcracks where a part of the potential energy is dissipated to heat, which may evoke, in a thermally insulated system, the initiation of microfires as primary centers of burning. The considered process is independent of the size of the coal body, humidity of the coal, and the degree of previous oxidation. A fundamental difference between this theory and other theories lies in the fact that a gradual increase in the coal temperature is not considered and that latent microfires occur directly.