An exact procedure for calculating the weight-average and number-average molecular weights of epoxy resins made by the advancement process is presented. The calculation can take into account the presence of high molecular weight diepoxides and monofunctional epoxides in diglycidyl ether of disphenol A and indicates that the presence of the latter has a very significant effect. A model for the taffy process based on the overall reactions of the process was developed. Analytical solutions could be obtained if the dehydrohalogenation reactions were assumed to be fast. The predictions of the model are in good agreement with the observed values reported earlier.