In this paper the examples of combined analytical methods usable for the characterization of thin film systems are presented. As the optical methods variable angle spectroscopic ellipsometry and spectroscopic reflectometry are used. It is shown that these methods can be employed for the complete determination of both the optical and material parameters of the materials forming the films. Moreover, it is shown that using the combined methods of AFM and the optical methods specified it is also possible to determine the values of the parameters characterizing some defects of the film systems under investigation. Discussion of the reliability of the methods enabling us to determine the values of the statistical quantities describing the boundary roughness of the thin films is also presented. A detailed attention is devoted to the results achieved for these quantities by atomic force microscopy for very finely rough film boundaries (i.e. nanometrically rough boundaries). The practical meaning of the combined methods presented is illustrated using the characterization of several samples of TiO2 films, hydrogenated polymorphous silicon films and oxide films originating by thermal oxidation of gallium arsenide substrates.