Ion beam irradiation of saturated polymers leads to the formation of new carbonaceous materials exhibiting enhanced electrical conductivity and increase of the optical absorption, which shifts gradually from the near UV to the visible. Different techniques, such as the analysis of the gas evolved from the polymer during irradiation, RBS and ERDA show the loss of the more volatile elements which results from the dissociation of the molecular structure. The consideration of different types of polymers indicates that some specific structural elements are preserved and that unsaturated bonds appear at high fluences, which are responsible for the loss of the insulating properties of polymers. The chemical bond modifications are discussed in view of infrared spectroscopy and ESCA, which shows the formation of graphite-like phases in polyimide and explains the high level of conductivity reached in this type of polymers. The appearance of conducting properties cannot be described by a simple model of carbonization and are governed both by the molecular structure of the parent polymer and the beam conditions. The behaviour of polyimide will be considered more in details because of the remarkable level of conductivity ( σ = 10 3 S/cm) and heat stability reached upon irradiation with heavy ions, which render this type of surface processing very efficient in order to produce conductive polymers.