AbstractSolidification and encapsulation of special wastes for disposal purposes. Apart from problems caused by special wastes due to their generally high content of harmful substances as well as other hazardous properties, difficulties in treatment and disposal of liquids, slurries and sludges are increased by their nonsolid state. Transformation of such special wastes into solid and largely non‐reactive products could offer a possibility of avoiding the difficulties at conventional disposal facilities. Solidification processes are also of interest in as much as they might open a way to dispose of such special wastes not only at special‐waste disposal facilities but also jointly with residential wastes at ordinary landfills. Recently solidification processes have been developed and are, in part, commercially applied in various countries. Utilisation or landfill disposal of the solidification products demand the definition of certain minimum requirements. Requirements with regard to water pollution prevention (e. g. leachability) are more difficult to formulate than other requirements unrelated to water protection (e. g. strength).