Poly(ethylene terephthalate) (PET) is a widely used thermoplastic polyester with excellent thermal and mechanical properties. It is a semicrystalline polymer with a glass transition temperature of 69°C and an equilibrium melting point of 280°C. PET's crystallization kinetics allow for the production of either a highly crystalline polymer for applications requiring high thermomechanical resistance and barrier properties or a fully amorphous polymer for high transparency. The crystallization process involves primary nucleation, crystal growth, and secondary crystallization, influenced by factors such as molar mass, catalyst residues, chain composition, and thermo-mechanical treatments. PET's crystal structure is triclinic, with a density higher than the amorphous form. The crystallization kinetics of PET are affected by various factors, including the presence of diethylene glycol (DEG) and other co-units, which influence thermal properties and crystallization behavior. PET can also be modified through copolymerization with other monomers, such as isophthalic acid (IPA) or 2,5-furandicarboxylic acid (FDCA), to tailor its crystallization kinetics and thermal properties. The crystallization of PET in blends and composites is influenced by the compatibility of the components and the addition of fillers, which can act as heterogeneous nucleating agents. The influence of plasticizers, water, and gases like carbon dioxide on PET's crystallization kinetics is also significant. The rigid amorphous fraction (RAF) plays a crucial role in determining the properties of semicrystalline polymers, with its formation and vitrification affecting the crystallization and mechanical behavior of PET. Overall, the crystallization of PET is a complex process influenced by various factors, and understanding these factors is essential for optimizing the properties and performance of PET in various applications.Poly(ethylene terephthalate) (PET) is a widely used thermoplastic polyester with excellent thermal and mechanical properties. It is a semicrystalline polymer with a glass transition temperature of 69°C and an equilibrium melting point of 280°C. PET's crystallization kinetics allow for the production of either a highly crystalline polymer for applications requiring high thermomechanical resistance and barrier properties or a fully amorphous polymer for high transparency. The crystallization process involves primary nucleation, crystal growth, and secondary crystallization, influenced by factors such as molar mass, catalyst residues, chain composition, and thermo-mechanical treatments. PET's crystal structure is triclinic, with a density higher than the amorphous form. The crystallization kinetics of PET are affected by various factors, including the presence of diethylene glycol (DEG) and other co-units, which influence thermal properties and crystallization behavior. PET can also be modified through copolymerization with other monomers, such as isophthalic acid (IPA) or 2,5-furandicarboxylic acid (FDCA), to tailor its crystallization kinetics and thermal properties. The crystallization of PET in blends and composites is influenced by the compatibility of the components and the addition of fillers, which can act as heterogeneous nucleating agents. The influence of plasticizers, water, and gases like carbon dioxide on PET's crystallization kinetics is also significant. The rigid amorphous fraction (RAF) plays a crucial role in determining the properties of semicrystalline polymers, with its formation and vitrification affecting the crystallization and mechanical behavior of PET. Overall, the crystallization of PET is a complex process influenced by various factors, and understanding these factors is essential for optimizing the properties and performance of PET in various applications.