Polyethylene terephthalate (PET), polyethylene (PE) polymers and diamond like coatings (DLC) have been treated with several plasmas with the purpose of incorporating different functionalities on their surface. Results with a dielectric barrier discharge (DBD) at atmospheric pressure, a microwave discharge at reduced pressure and those using an atom source working under high vacuum conditions with several plasma gas mixtures have been compared. The incorporated functional groups at the surface have been monitored by X-ray Photoemission Spectroscopy (XPS). Special emphasis has been paid to get oxygen and carbon depth profiles for the plasma treated surfaces by the so-called XPS peak shape analysis, a non-destructive method that allows the determination of compositional in-depth (up to 6–8 nm) profiles. The surface topography of the treated samples has been examined by Atomic Force Microscopy, while the surface tension has been determined by measuring the static contact angles of water and iodomethane. Thus, for example, it is found that a DBD treatment with Ar/NH3 mixtures is very efficient for nitrogen and amine group surface functionalization. It is also realized that the nitrogen functional groups do not contribute significantly to the observed increase in surface tension of plasma treated surfaces. On the other hand, oxygen plasmas produce on DLC only weak surface oxidation but considerable increase of hydrophobicity. We have established correlations between the changes induced at the surface (chemical, topographic, wettability) with the intrinsic characteristics of the activation plasma processes.