The objective of this work is to study polymer/surfactant interactions in aqueous solution and at the air/water interface. These interations are involved in many physicochemical phenomena, such as colloidal stabilization and wettability which are of major importance in oil application as for exemple drilling muds. More precisely, we have attempted to characterize interactions between a non surface active anionic copolymer (acrylamide/acrylamide sulfonate) and an oppositely charged cationic surfactant (C(12)TAB). Our results show a synergestic surface tension lowering (coadsorption) at extremely low surfactant concentrations (10(-3) to 10(-1) CMC). At higher concentrations, namely above the so called Critical Aggregation Concentration (CAC), polymer-surfactant complexes form in the bulk and the macromolecules precipitate out of the solution. Foam films made from these mixed solutions are stable while C(12)TAB films are unstable. Disjoining pressure measurements on mixed films with surfactant concentration two orders of magnitude below the CAC show the existence of long range repulsive forces and a discrete film thickness transition. At the CAC, we obtain mixed films with gel-like networks that are strongly affected by the film thinning rate.