Depending on the conditions, isotactic Polypropylene (iPP) can form different crystalline phases. This can be clearly observed in injection molding samples. Using X-ray scattering methods, a distribution of four different phases (α, β, γ, meso) over the thickness of the sample is found. From several experimental methods, including extended dilatometry (PVT) the multi-phase, multi morphology (shish-kebab, cross-hedging also known as parent and daughter structures) crystallisation kinetics were determined. Next, we used a prototype industrial flow device (piston driven slit flow) combined with in situ wide angle X-ray diffraction and small angle X-ray scattering to measure the evolution of the (oriented) crystalline structures and phases (α, β, γ) for different flow conditions. We developed an accurate numerical model able to describe flow induced crystallization of isotactic polypropylene at high pressures and shear rates. The finite element model includes a full coupling of nonlinear viscoelasticity, compressibility, non-isothermal flow and flow induced crystallization equations. The slit flow is used as a test case that is simulated at a wide range of imposed pressures and piston speeds. The build up and relaxation of the pressure difference and the development of the different structures and phases during and after flow are accounted for. Quantitative agreement with experiments is obtained. To our knowledge, this is the first time that such an extended modeling is presented.