The concept of “Green Chemistry” and the demand for sustainable chemical syntheses are currently leading to a renaissance of tribochemical or mechanochemical reactions. This type of reaction management often completely avoids the use of solvents and temperature treatments. Reactions are initiated by impact, friction, or shear forces of grinding bodies. The reactors used are usually mills, originally designed for the simple grinding and crushing of solids. This chapter discusses different mill concepts, explains important process parameters, and gives examples of how these are used in tribochemical reactions in current research.