An ellipsometric approach is described for interpreting polarization information in surface second harmonic generation (SHG). The general applicability of nonlinear optical ellipsometry (NOE) was demonstrated in SHG measurements of uniaxial films under resonant, near-resonant, and nonresonant conditions. The modularity inherent in the instrumental design allows the same basic mathematical formalism to be used to describe a diverse array of optical configurations for polarization analysis. This methodology is particularly useful in spectroscopic and resonance-enhanced SHG and SFG measurements, in which intensity-based methods are generally not applicable. In one application, SHG polarization measurements were used for what is believed to be the first time to measure ratios of the dominant elements of the tensor describing two-photon absorption.