The present work deals with two different surface modification techniques for altering the surface properties of polymers: plasma treatment and ion implantation. Polymer foils were exposed in an inductively-coupled r.f. (13.56 MHz) plasma system with and without applying a negative high voltage pulse to the sample stage. The influence of low pressure plasmas of oxygen, nitrogen, or argon on the chemical composition, topography, and wettability of polymer surfaces was studied in detail. Etch rates of poly(ethylene terephthalate) for different plasma parameters were monitored. The polymer surface was also modified by a high energy ion beam process. Polyimide films were implanted with different ion species such as Ar+, N+, C+, He+, and O+ at doses from 1 x 10(15) to 1 X 10(17) ion/cm(2). Ion energy was varied from 10 to 60 keV for the plasma source ion implantation (PSII) experiment. Polyimide samples were also implanted with 1 MeV hydrogen, carbon, and oxygen ions at a dose of 1 x 10(14) ion/cm(2). Depending on the ion energy, dose, and ion species, the surface resistivity of the film was reduced by several orders of magnitude. A study on the plasma-treated and ion beam-treated polymer surfaces was performed using TOF-SIMS, XPS, SEM, AFM, and water contact angle measurements.