The surface free energy of a polymer can be easily calculated by the Group Contribution Method developed by the authors. After having briefly recalled the method and illustrated it with new examples, the latest developments including the Weighted Group Contribution Method and the study of the molecular weight dependence of surface free energy are also expounded. Finally, very simple means to determine the dispersive contribution to the surface energy are described. The dispersive component values calculated from the Lifshitz theory, and from the solubility parameters, are in good agreement with those obtained from wettability measurements.