Using an extensive database that covers activity coefficients in systems of polymers and copolymers with nonpolar and polar solvents, we test the predictive capabilities of two simple activity coefficient models: the Entropic-FV (free volume) and a recent modification of UNIFAC by Zhong et al. (Fluid Phase Equilib. 1996, 123, 97). The only information required for their application is the structure of the components and in the case of Entropic-FV also their molar volumes. The results, which include solvent and polymer activity coefficient predictions (the latter based on data from molecular simulation), indicate that both models provide satisfactory predictions-except where association is present-considering their simplicity, with the Entropic-FV one being superior to the modified UNIFAC proposed by Zhong et al. The latter, however, is a very good alternative when no accurate molar volumes are available.