Various methods for predicting the thermodynamic behavior of paint-related and other complex polymer solutions are investigated. Both the methods currently used in the paint industry for solvent screening, and other rule-of-thumb based methods, are shown to be good tools for identifying suitable solvent for a polymer resin. If, e.g., phase diagrams need to be predicted, more sophisticated models has to be considered, such as activity coefficient models and equations of state based on group-contribution. Such models are shown to represent the experimental thermodynamic data satisfactorily well, which indicates that these may be further developed to represent even more complex systems and types of phase-equilibria.