After a brief review of some fundamentals of thin-film light guides, the dispersion and the attenuation of an ideally smooth light-guiding dielectric film are presented as weighted averages of the bulk dielectric properties of the three materials forming the guide (substrate, film, and superstrate). The weights entering here are essentially the fractions of the electric field energy travelling in each of the materials. In a real guide, the light-guiding properties are also affected by any nonuniformities of the film thickness. These considerations are applied to the light-guiding films required for various purposes of integrated optics. Conversely, it is shown how measurements of the light-guiding properties of a film may help to determine other characteristic parameters of the film. In the last section the numerous methods are reviewed that have been used for the preparation of light-guiding films.