The review reflects the results of theoretical and experimental investigations of thin dielectric films with an aim of using them to develop integrated optical circuits. The principal properties of optical waveguides on dielectric substrates are considered. Methods are analyzed for the admission and extraction of light through the waveguide surface using the optical tunnel effect, using a phase diffraction grating, and using a gradually tapering edge. Attention is paid to the conversion of the frequency of laser radiation in a nonlinear thin-film waveguide, and also to the losses due to absorption and scattering of light in the films. The review describes, in addition, the principal results of theoretical and experimental research on the interaction of optical and acoustic waves in thin films, and on amplification and generation of light in activated thin-film waveguides. Passive optical elements based on thin films are also considered.