If polymer materials are now so widely used that it is hard to imagine life without them - billions of kilograms of plastics are sold every year-, a significant set of applications rests on polymers in juxtaposition with another material, as in composites or (multi)layered structures. All properties of these ensembles depend on successful and controlled adhesion, a very complex technology indeed that encompasses various physico-chemical interactions between two surfaces. This presentation will review the different methods used in the laboratory, or at the production plant, to modify, if possible in a very controlled way, a polymer surface. To remove superficial contamination, to modify surface morphology, to tune hydrophobicity, to functionalize a polymer surface ... can be achieved by various chemical or physical methods. Surface treatment is particularly versatile when using a plasma discharge, a vacuum technique, while X-Ray Photoelectron Spectroscopy (XPS) appears a method of choice to control the tailored polymer surface. Potentials of the cold (reactive) plasma treatment will be shown; advantages and problems of the XPS characterization method will be pointed out; complementary information gained by FT-infrared and contact angle measurements will be illustrated. Two sample cases will be commented on: (1) plasma treatment of polyester, in various reactive gases that shows ageing (surface oxidized species slowly disappear with time), while an optimum amount of functionalization allows better adhesion of an evaporated aluminium layer (mechanical adhesion test); (2) some parameters governing the physico-chemical interactions at the SiO@sub x@ -functionalized polypropylene interface will be explained with the help of the acid-base concept.