The fate of heavy metals is one of the main problems that operators of solid waste incineration plants have to deal with to reduce the overall environmental impact of the plant and of the ultimate residue. The question is : should the process conditions avoid toxic metal vaporisation, thus increasing their concentration in bottom ash ? Or, on the contrary, should they favour metal release in combustion gases, thus requiring the highest performance air pollution control (APC) systems and stabilising materials? In order to examine the industrial impact of these two possibilities, we are currently developing two complementary approaches.The first one is concerned with the fate of heavy metals in incineration of municipal wastes and sludge, and coal combustion. We characterised physico-chemically the ultimate residues, and we developed a complete thermodynamic and experimental study of the behaviour of heavy metals in waste incinerators and coal combustors. We developed a general method (inverse method) to identify the kinetics of vaporisation of heavy metals from the on-line analysis of the exhaust gas of solid waste incineration. The second approach deals with the transformation of heavy metals contained in fly ash and dredged materials into phosphate components, using orthophosphate as stabilising agent.The technique involves a chemical treatment followed by a thermal treatment (sintering), that reduce the leachability of heavy metals. Better knowledge of thermal treatment of polluted wastes should lead to safer processes and residue reuse opportunities.