In order to understand crystallization behavior and to predict polymer resin properties, crystallization kinetics and morphology studies are performed. Thermal analysis of sixteen polyethylene and polypropylene resins was carried out, using Differential Scanning Calorimetry (DSC) to study the crystallization kinetics and mechanism of crystallization. Attention is given to different polyethylene grades, particularly linear low-density polyethylenes (LLDPE) manufactured with Ziegler-Natta and metallocene catalysts. The polymers are obtained with different monomers (1-butene, 1-hexene or 1-octene). Some polymers are based on gas phase polymerization, while others are based on solution polymerization. The isothermal crystallization data were treated to account for transients and to compensate for instrument errors. The data were fitted to the Avrami and Tobin equations, and the corresponding kinetic parameters are reported. The non-isothermal data were fitted to the Ziabicki equation, in order to determine the relevant parameters. Subsequently, the non-isothermal data were compared to the predictions of the Nakamura equation, with good agreement. An effort was made to compare the isothermal and non-isothermal crystallization behavior of the various resins to evaluate the effect of co-monomer and catalyst type. The results indicate significant differences among the resins, and reveal the utility of the DSC as a tool for distinguishing the characteristics of the various resins.