Processes using crystallisation from a supercritical, medium constitute a new route to obtain finely divided solids. By using the pressure as an operating parameter, these processes allow to obtain fine and monodisperse powders. There exist two types of processes, according to whether supercritical fluid usually carbon dioxide - is used as a solvent or an anti-solvent: RESS or SAS. In the first case it is the drop in density due to the brutal decompression of the fluid which is the driving force of nucleation, in the second it is the reciprocal dissolution of an organic solvent in the supercritical fluid. Industrial applications are expected in many sectors, even if it is the pharmaceutical industry which seems best armed to gather a majority of its developments.