Poly(ethylene terephthalate) (PET) is a widely used thermoplastic polyester known for its excellent thermal and mechanical properties. Its semicrystalline nature allows for easy control over crystallization kinetics, which is crucial for producing PET with high thermomechanical resistance, barrier properties, or high transparency. The polymer's crystallization process involves primary nucleation, crystal growth, and secondary crystallization. The crystallization kinetics are influenced by factors such as molar mass, catalyst residues, chain composition, and thermo-mechanical treatments. PET crystallizes from the melt with a spherulitic morphology, and its crystallization rate is maximized around 160-180°C. The crystallization rate is affected by the polymer's molar mass, the presence of diethylene glycol (DEG) side groups, and the type of catalyst used. Chain branching and the addition of fillers can also impact crystallization behavior. Blending PET with other polymers or incorporating fillers can modify its crystallization properties. The formation of a rigid amorphous fraction (RAF) during crystallization further influences the polymer's properties, affecting barrier and mechanical performance. Understanding these crystallization processes is essential for optimizing PET's performance in various applications.Poly(ethylene terephthalate) (PET) is a widely used thermoplastic polyester known for its excellent thermal and mechanical properties. Its semicrystalline nature allows for easy control over crystallization kinetics, which is crucial for producing PET with high thermomechanical resistance, barrier properties, or high transparency. The polymer's crystallization process involves primary nucleation, crystal growth, and secondary crystallization. The crystallization kinetics are influenced by factors such as molar mass, catalyst residues, chain composition, and thermo-mechanical treatments. PET crystallizes from the melt with a spherulitic morphology, and its crystallization rate is maximized around 160-180°C. The crystallization rate is affected by the polymer's molar mass, the presence of diethylene glycol (DEG) side groups, and the type of catalyst used. Chain branching and the addition of fillers can also impact crystallization behavior. Blending PET with other polymers or incorporating fillers can modify its crystallization properties. The formation of a rigid amorphous fraction (RAF) during crystallization further influences the polymer's properties, affecting barrier and mechanical performance. Understanding these crystallization processes is essential for optimizing PET's performance in various applications.