Undesired moiré patterns may appear in color printing for various reasons. One of the most important reasons is interference between the superposed halftone screens of the different primary colors, due to an improper alignment of their frequencies or orientations. We explain the superposition moiré phenomenon using a spectral model that is based on Fourier analysis. After examining the basic case of cosinusoidal grating superpositions we advance, step by step, through the cases of binary gratings, square grids, and dot screens, and discuss the implications on moirés between halftone screens in color separation. Then, based on these results, we focus on the moiré phenomenon from a different angle, the dynamic point of view: We introduce the moiré parameter space and show how changes in the parameters of the superposed layers vary the moiré patterns in the superposition. This leads us to an algorithm for moiré minimization that provides stable moiré-free screen combinations for color separation.