The microkinetics of crystallization and the melting behavior of solid-state polymerized poly(ethylene terephthalate) (PET) have been studied. After correlating crystallization data with secondary nucleation theory and a single regime of growth, a positive correlation was found between molecular weight, free energy products, and transport activation energy. The results indicate that the crystallization behavior of PET might be correlated with regime III if the secondary nucleation theory is assumed to apply. They also support a model of crystallization involving primary and secondary crystallization with increased branching when the molecular weight increases. The melting behavior of PET, previously studied at commercial levels of molecular weight, and proposed before as morphologically the reverse of the crystallization process (Medellin-Rodriguez et al. J Poym Sci B Polym Phys 1997, 35, 1757), continues with solid-state polymerized PET. In particular, it was observed that the second melting endotherm continues to increase with the molecular weight, the process involving a proportional decrease of the third endotherm. This characteristic continues even up to levels where only the first and second melting endotherms are present. The first melting endotherm was also studied, and the results indicated that it is probably related to low molecular weight segregated fractions.