Sculptured thin films (STFs) are nano-engineered materials that have controllable porosity, structural chirality, and periodicity in one, two, or three dimensions. They have been exploited in developing optical elements such as thin-film filters, polarizers, sensors, and waveguides for integrated optics. A grating theory-based modeling approach for STFs as fully three-dimensional (3-D) periodic structures is developed. Input for this model consists of a structural parameter set that is easily accessible experimentally. This parameter set is common to evaluating STFs from a fabrication as well as modeling perspective and thus furnishes a basis for developing appropriate process monitoring and control methods necessary for successful commercial production. Using the proposed model, a quantitative understanding of the limits of applicability of traditional modeling methods for STFs and guidelines for robust design of STF-based devices are developed. This knowledge gained is applied to explore STFs in two illustrative examples: (1) as a notch filter and (2) as a 3-D photonic crystal.