The solubility of liquid molecules in glassy polymers has been considered by using the general results of the Non-Equilibrium Thermodynamics of Glassy Polymers (NET-GP), which proved successful to calculate solubility isotherms of gases in glassy polymers for rather different situations, including polymer blends, mixed gases, and mixed matrices. It is shown that the existing model is suitable also for liquid penetrants in a glassy phase: water and ethanol sorption in polycarbonate (PC) and water sorption in polysulfone (PSf) have been examined as examples. The model's ability to predict the solubility from both liquid and vapor phases was tested successfully, using the same values of the parameters for both phases. In the case of PC, the model was also applied to calculate successfully the solubility of liquid water at different temperatures from 25 to 130 degrees C, with a single value of the energetic binary parameter. (C) 2011 American Institute of Chemical Engineers AIChE J, 58: 292-301, 2012