The mechanism, synthetic application, scaling, and industrial production with gas-solid and solid-solid reactions without producing wastes is outlined. These reactions profit from lowered activation energy (with respect to melt reactions), favorable kinetics with definite end of reaction, and mostly reaction specificity giving only one product in pure form without workup necessity. They proceed thus solventless (not only "solvent free") and wasteless. The bargain of the solid-state should not be given up by heating to melt (e.g., milling without temperature control) or by "adding a little solvent". Molecular (or ionic) solid-state reactions, be they gas-solid or solid-solid, profit from the presence of cleavage- planes, channels or voids for intracrystalline long-range anisotropic molecular migrations. Such release of internal local pressure upon chemical change is essential. This is experimentally verified. In the solid-solid case mixing and contacting leads to the thermodynamically more stable product, but this does not exclude kinetic control. It is of utmost importance to control the temperature so that eutectic temperatures (melts) are not reached during all reaction stages. Typical examples out of more than already thousand 100% yield reactions from 26 reaction types for particularly delicate (not otherwise available) or otherwise interesting products are presented, and the scaling up to continuous industrial production is exemplified. Also, mechanochemical reactions (for example counter- thermodynamic mechanical bond breaking of infinite covalent materials) can be waste-free, ending with the most stable possibility when the bond-breaking ceases at the nanoscale. The proper experimentation (most important is strict temperature control) is outlined and easily and safely achieved.