Until the 1990s, technology was the main driver when dealing with waste and residues, the objective being the treatment of waste for (landfill) disposal, storage, and in some cases sorting. In the 1990s, depletion of raw materials and socio-economical concerns supported the direct recycling of waste and residues. However, the direct recycling approach is limited when waste/residues contain significant amounts of pollutants such as heavy metals and organics (VOC, PAH), and when the treatment process to remove/stabilize or destruct the pollutant generates emissions. Due to depletion of natural resources, increasing greenhouse emissions, and awareness of the need for sustainable development in terms of safely reusing waste and biomass, the transformation of waste/biomass to valuable materials and energy (i.e. valorization) is emerging as a strong trend.