Planetary ball mills serve as reactors for homogeneous or heterogeneous mechanochemical reactions. The milled material is crushed by high-energetic impacts and friction of the milling balls and the grinding chamber walls. Important factors for the efficiency of a high-energy ball milling process are the proportion of the masses (powder to milling ball mass ratio), the geometric parameters of the mill, the duration of the milling process and the rotational frequency. Planetary ball mills are usually used for the batched particle size reduction to ultrafine particle sizes of materials (nanomaterial) of various hardnesses, dry or in a suspension, also for mixing and homogenisation of powders (e.g. mechanical alloying), emulsions and pastes. Many parameters have to be controlled to have reproductive results. In modern ball mills for example interval and pause times or a reverse automatic for special applications can be programmed. For laboratory use grinding chambers from 40 to 500 ml of volume are reasonable. For the milling of oxidizable material, special lids for the application of inert gas atmospheres have to be used. Gas pressure and temperature development during the milling process can be observed and recorded using the GTM system.