This paper qualitatively describes the principles and presents some applications of the rapidly developing technique of automatic spectroscopic ellipsometry, as applied to the analysis of the properties of surfaces and interfaces of materials in bulk or thin film form. Examples include composition and density measurements of polycrystalline and amorphous Si films, the determination of the best-quality surfaces of bulk materials, oxidation of Si, optical profiling of microscopic surface roughness, determination of interface widths in semiconductor–oxide systems and CVD heterostructures, and nucleation of a-Si films.