The production of carbon nanostructures at very high temperature by thermal plasma has been one of the major research areas developed by Ecole des Mines de Paris and CNRS in association with industrial companies for more than ten years. Thermal plasmas allow operating conditions that cannot be achieved by conventional combustion processes (temperature, atmosphere) since the enthalpy is given by an external energy supply (plasma arc) in the total absence of oxygen which leads to a totally clean process (zero emission). Researches carried out on a semi-industrial pilot reactor have shown that thermal plasmas were particularly adapted to the production of carbon based nanomaterials and have demonstrated their enormous potentials in this field. The plasma technology is characterized by a high versatility since it can be used for the synthesis of a wide range of carbon nanostructures ranging from Carbon Black over Fullerenes to carbon nanotubes with a high product selectivity, using a wide range of liquid, gaseous or solid carbon precursors.