Composts may contain organic pollutants (OPs) because of their presence in feedstock materials. Numerous studies have reported the dissipation of OPs during composting. Indeed, they are susceptible to be degraded, volatilized, lixiviated or stabilized through sorption interactions with waste organic matter, culminating with the formation of non-extractable residues (bound residues). In this case, the availability of OPs is reduced although biodegradation is the only true mechanism of OP elimination. It is necessary to use 14C-labeled OPs in order to make a distinction between these phenomena which have been poorly characterized in the literature. In this work, we characterized and modeled the evolution of OP speciation during the composting of organic wastes in order to estimate OP availability in final composts and provide information to better assess environmental impacts related to compost use on cultivated soils. The use of 14C-labeled OPs made it possible to assess the evolution of OPs during the composting of a sewage sludge and green waste mixture. Four OPs representing some of the major groups of OPs detected in composts were used: a polycyclic aromatic hydrocarbon (fluoranthene), two surfactants (4-n-nonylphenol, NP, and sodium linear alkylbenzene sulfonate, LAS) and a widely used herbicide (glyphosate). An experimental set-up including six small-scale composting pilots was built. It was used to simulate the composting process with a good reproducibility, at a size compatible with the use of 14C-OPs. Six composting experiments were first carried out, without 14C-OPs addition. The compost materials were sampled at different stages of composting in order to assess compost sorption properties, as well as the potential for compost microflora to degrade OPs using incubation experiments with 14C-OPs addition. The results showed that i) the active composting phases should be favored to maximize the biodegradation of simple molecules (such as glyphosate, LAS and NP) and ii) the duration and maintenance of good conditions for microbial activity during maturation are essential for the optimal degradation of complex molecules with fused aromatic cycles (such as fluoranthene). Sorption decreased as compost maturity increased, except for glyphosate. No relationship was found considering the four OPs between sorption and total OP mineralization. Secondly, 12 composting experiments with 14C-OPs addition on the initial mixture at the beginning of composting were performed in order to assess the evolution of OP speciation during composting. The dissipation of LAS was largely due to mineralization. For NP and glyphosate, both mineralization and formation of non-extractable residues appeared to equally contribute to dissipation. For fluoranthene, the dissipation was only related to non-extractable residues formation. Composting appeared as an effective treatment reducing the direct availability of OPs and thus the related dissemination risks when composts are used on agricultural soils. The extent of non-extractable residue formation was however high for NP and glyphosate and the amounts of potentially available OPs after desorption were moderate for glyphosate and high for fluoranthene. A model called COP-Compost was developed to simulate the C of organic matter and Organic Pollutant evolutions during COMPOSTing. It included two modules. The first one simulated the evolution of microbial populations and the biochemical transformations of the organic matter during composting. It was parameterized and validated using data found in the literature. The second one described the evolution of the OP speciation and mineralization during composting. It was calibrated using experimental data of the present work. Three coupling hypotheses describing the interactions between the two modules were proposed. The first one stipulated that the overall OP sorption on the organic matter would be the sum of the individual sorption on the different biochemical fractions of organic matter. This hypothesis could not be validated with the experimental data. The second and third hypotheses, specifying that the OP biodegradation and the formation of non-extractable residues would be dependent of the overall microbial activity driven by organic matter decomposition, were validated.