The crystal stucture of crystalline solids is drastically changed by intensive mechanical forces: permanent lattice defects, polymorphic tranformations, total amorphisation, possible homogeneous chemical reactions, and a definite increase of surface free energy can be observed; all these phenomena show that a high share of grinding energy can be permanently stored in the ground material.:Due to this mechanical activation the solid will be capable of surface and solid-state reactions, and consequently the dispersity of the system is decreased irreversibly and both the phase composition and chemical composition are changed in the direction of increased system stability. Novel type mechanochemical "capillary" reactions are also described. Reactions and surface interactions can be modified to a certain extent by vapour adsorption. Thermal and adhesion properties of solids, exposed to intensive grinding and being in an active state or having been subjected to mechanichemical transformations, are drastically changed; this change may influence several technologies involving grinding.