Flow induced crystallization is an important process during polymer solidification because it strongly influences the material morphology and properties. The melt of isotactic polypropylene crystallizes slowly in quiescent conditions whereas sheared conditions speed up the crystallization process. The main objective of the presented research is the investigation of the shear-induced crystallization of isotactic polypropylene through a comparative analysis between quiescent and non-isothermal conditions in different shear regimes. We use data coming from differential scanning calorimetry (DSC) and a polarized optical microscope (POM) mounted on a rotational rheometer. The polypropylene morphology is recorded during the experiment using the POM for small strain amplitude oscillatory measurements and DSC to evaluate the crystallization degree and the microstructure before and after the shearing. A numerical simulation of crystallization kinetics of semicrystalline thermoplastics with a multiscale model is also proposed to evaluate the nucleation and growth of spherulites, after identifying the analytical parameters needed to connect crystallization kinetics with molecular material properties. Keywords: Polymer, Crystallization, Numerical Simulation.