The preparation of Nylon-6 via the initiated anionic polymerization of EE-caprolactam is characterized by rapid reaction rates displaying marked auto-acceleration. A mechanistic approach has been taken to analyze the kinetics of this system and has resulted in the postulation that the auto-acceleration is directly linked to a polymer chain degradation reaction. This reaction is significant even in the early stages of the polymerization and in many cases becomes the dominant mechanism for the production of reactive end groups, thereby controlling the overall reaction rate. A kinetic model is presented which is capable of differentiating between polymerizations carried out with different levels and ratios of catalyst and initiator, and contains but two rate constants—one for the propagation reaction and one for the degradation reaction. Predictions of the model are compared to experimental rate data derived from using both mono-and difunctional initiators and close agreement is found.