Spectroscopic ellipsometry and spectral photometry have been applied for the deposition of optical coatings on architectural glass. For the purpose of achieving a high competitiveness of manufacturing plants, high deposition rates as well as low scrap quantities are important. The first can be obtained by using the mid-frequency (MF) sputtering technique developed at the beginning of the 1990s for the deposition of highly isolating materials. The latter can be improved by using an effective plasma control and a monitor of the optical film properties. In order to obtain constant layer properties, not only the MF but also the direct-current (DC) sputter process has to be stabilized within a relatively narrow process window, which necessitates a suitable plasma control as well as optical monitoring. Spectroscopic ellipsometry as well as spectral photometry are used for monitoring the optical properties of SnO2-based low-e-coatings on architectural glass. It is shown that spectroscopic ellipsometry is distinctly more sensitive for monitoring the thickness of low-e coatings than spectral photometry.