Ellipsometric measurements at multiple wavelengths from the UV-Vis to IR region and/or variable angles of incidence provide large data sets of Δ,Ψ -pairs to characterize a wide set of interfacial states of organic layers with the capability of crosschecking the assumed optical model. More and more complex optical models are applied to describe the real surface state and nature of the organic layers: Effective medium approaches, Cauchy relations for nonabsorbing and oscillator parametrizations for absorbing as well as anisotropic models for oriented layers are useful for optimum fitting of the data from Variable Angle Spectroscopic Ellipsometry (VASE).