A kinetic model has been developed for the formation of selected congeners of PCDD/Fs during the thermal decomposition of different wastes in a horizontal reactor. Previously published data on the decomposition of wastes have been correlated using a kinetic model that only considers process parameters, such as the presence of different amounts of oxygen in the atmosphere of reaction, chlorine and metals in the waste. The effect of both chlorine and metals is modelled through an equation assuming a “saturation effect”, i.e., that a certain amount of each substance produces the maximum rate, and that higher amounts do not increase the rate. The presence of oxygen is modelled by a destruction reaction over part of the PCDD/Fs produced. The model, which uses data from more than 64 experiments, correlated the emissions of three selected congeners: 1,2,3,6,7,8-HxCDD, OCDF and 2,3,7,8-TCDF, which are enough to estimate the total amount and toxicity of an emission.