CF4 plasma treatment of a range of polymers (polyethylene, polypropylene, polyisoprene, polystyrene, polyether ether ketone, polyethylene terephthalate, polycarbonate, polysulfone, and polyether sulfone) has been investigated by X-ray photoelectron spectroscopy (XPS). A correlation is found to exist between the level of fluorine incorporation into the surface and the chemical structure of the parent polymer. This experimental observation can be rationalized on a theoretical basis in terms of results obtained from extended Huckel molecular orbital calculations.