Xylene is an aromatic hydrocarbon commonly used in industry as a solvent, but it is also one of the most widely utilized precursors for large-scale production of carbon nanostructures, such as nanotubes, carbon nanofibers or graphene. The carbon feed mechanisms strongly influence the morphology and the quality of these materials. To improve the yield and allow a better control of the synthesis process, a thorough understanding of the chemical kinetics is needed. Hence, the thermal decomposition of xylene was experimentally and numerically studied at temperatures ranging between 500 and 900°C and under atmospheric pressure. The products and kinetics of the xylene pyrolysis were in situ investigated by mass spectrometry and gas phase chromatography and a detailed mechanism was postulated to account for the main products. The evidence of synergistic effects on the xylene decomposition due to the addition of hydrogen and/or acetylene was demonstrated. These results were then applied to the synthesis of various multi-scale hybrid structures for a wide range of applications.