The motives for carrying out chemical processes in supercritical fluid solutions are outlined. Variation of pressure and temperature within extended ranges allows to optimize reaction conditions with respect to chemical kinetics, transport properties and phase behaviour. Free-radical polymerization in the fluid phase provides the additional advantage of continuously tuning the properties of the polymeric material by changing reaction pressure and temperature. Examples of novel fluid phase reactions are presented ,together with kinetic studies of free-radical polymerization up to kbar pressures.