Three-component emulsion polymer systems constitute an overall four-component system from a morphological viewpoint. The aqueous phase is always the continuous phase within which 22 distinct and thermodynamically stable particle morphologies may exist. Six uniquely different categories of particles compose this morphological menu and may be identified as core–shell–shell, hemicore, hemishell, trisectional, “snowman,” and cored hemisphere. Extension of previously published free-energy thermodynamic analyses of two component emulsion polymers has resulted in the ability to predict the most likely equilibrium morphology to be found for three-component particles. Predictions have been carried out for each possible three-component combination of poly(methyl methacrylate), polystyrene, poly(dimethyl siloxane), and polycarbonate. The results show that in nearly every instance two or three different morphologies are computed to possess nearly equivalent free energies, whereas all other possibilities would result in much higher free energies. This indicates that more precise knowledge of all interfacial tensions is required when considering three-component systems than was found to be generally needed for two-component systems. Experiments were carried out for each polymer combination using a very surface-active emulsifier (sodium lauryl sulfate) and, separately, a weakly surface-active emulsifier (natural pectin). For this choice of polymers and emulsifiers, only three of the six unique morphological categories were found experimentally. In all cases, the thermodynamic analysis predicted the experimentally determined morphology to possess the lowest or next to lowest free energy. © 1993 John Wiley & Sons, Inc.