Valuable information on the phenomenology of mechanical activation will be obtained from the accurate characterization of wearing processes that take place within mechanochemical reactors. Favoring the contamination of reactant powders with material from a reactor’s debris, for a long time such processes represented one of the greatest limitations to practical mechanochemistry applications. We will focus on two related aspects of mechanochemical processing by grinding in a ball mill: (i) nanoscale wear of the treated substances and of the milling tools (balls and container wall); and (ii) deposition of a powder coating on the surface of the milling tools (self-lining phenomenon). A new technology called abrasive-reactive wear (ARW) has been developed that utilizes wear debris as an integral component of the reaction system rather than treating it as a harmful impurity. This technology is applied to the preparation of nanocomposites and to the processing of mineral raw materials and industrial byproducts. This review includes preparation experiments, material characterization, ARW kinetics and simulation. Besides developing new technologies, ARW will contribute to a better understanding of the mechanochemical or mechanical alloying process in general.